refactor: flatten skills/ and adopt Agent Plugins 1.0

The Agent Plugins standard reads only the immediate children of
skills/ and cannot be pointed elsewhere, so a bucketed tree is
invisible to every conformant client.

Rather than generate a flat copy of the repo into a package
directory — a builder, a validator, an allowlist, a drift CI job,
and every skill committed twice — remove the buckets.

- skills/ is flat and holds exactly the promoted 25
- in-progress/ -> drafts/, misc/ -> extras/, deprecated/ deleted
- new root plugin.json (Agent Plugins 1.0)
- .claude-plugin/plugin.json loses its 25-entry skills array
- docs/ keeps its category folders; it is now the only place a
  skill's category lives

Reasoning in .agents/adr/0003.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

README.md

@@ -97,8 +97,8 @@ This is just the same in the AI age. There is a communication gap between you an
 
 **The Fix** is to use:
 
-- [`/grill-me`](./skills/productivity/grill-me/SKILL.md) - for non-code uses
-- [`/grill-with-docs`](./skills/engineering/grill-with-docs/SKILL.md) - same as [`/grill-me`](./skills/productivity/grill-me/SKILL.md), but adds more goodies (see below)
+- [`/grill-me`](./skills/grill-me/SKILL.md) - for non-code uses
+- [`/grill-with-docs`](./skills/grill-with-docs/SKILL.md) - same as [`/grill-me`](./skills/grill-me/SKILL.md), but adds more goodies (see below)
 
 These are my most popular skills. They help you align with the agent before you get started, and think deeply about the change you're making. Use them _every_ time you want to make a change.
 
@@ -128,7 +128,7 @@ This concision pays off session after session.
 
 </details>
 
-This is built into [`/grill-with-docs`](./skills/engineering/grill-with-docs/SKILL.md). It's a grilling session, but that helps you build a shared language with the AI, and document hard-to-explain decisions in ADR's.
+This is built into [`/grill-with-docs`](./skills/grill-with-docs/SKILL.md). It's a grilling session, but that helps you build a shared language with the AI, and document hard-to-explain decisions in ADR's.
 
 It's hard to explain how powerful this is. It might be the single coolest technique in this repo. Try it, and see.
 
@@ -153,9 +153,9 @@ It's time to look at your feedback loops. Without feedback on how the code it pr
 
 For automated tests, a red-green-refactor loop is critical. This is where the agent writes a failing test first, then fixes the test. This helps give the agent a consistent level of feedback that results in far better code.
 
-I've built a **[`/tdd`](./skills/engineering/tdd/SKILL.md) skill** you can slot into any project. It encourages red-green-refactor and gives the agent plenty of guidance on what makes good and bad tests.
+I've built a **[`/tdd`](./skills/tdd/SKILL.md) skill** you can slot into any project. It encourages red-green-refactor and gives the agent plenty of guidance on what makes good and bad tests.
 
-For debugging, I've also built a **[`/diagnosing-bugs`](./skills/engineering/diagnosing-bugs/SKILL.md)** skill that wraps best debugging practices into a disciplined loop, gated phase by phase.
+For debugging, I've also built a **[`/diagnosing-bugs`](./skills/diagnosing-bugs/SKILL.md)** skill that wraps best debugging practices into a disciplined loop, gated phase by phase.
 
 ### #4: We Built A Ball Of Mud
 
@@ -173,9 +173,9 @@ For debugging, I've also built a **[`/diagnosing-bugs`](./skills/engineering/dia
 
 This is built in to every layer of these skills:
 
-- [`/to-spec`](./skills/engineering/to-spec/SKILL.md) quizzes you about which modules you're touching before creating a spec
+- [`/to-spec`](./skills/to-spec/SKILL.md) quizzes you about which modules you're touching before creating a spec
 
-And crucially, [`/improve-codebase-architecture`](./skills/engineering/improve-codebase-architecture/SKILL.md) surveys a codebase for deepening opportunities and hands you the candidates. I recommend running it on your codebase once every few days. It is a survey, not a rescue: on a genuinely old codebase it will find real candidates, but it won't untangle the mud for you.
+And crucially, [`/improve-codebase-architecture`](./skills/improve-codebase-architecture/SKILL.md) surveys a codebase for deepening opportunities and hands you the candidates. I recommend running it on your codebase once every few days. It is a survey, not a rescue: on a genuinely old codebase it will find real candidates, but it won't untangle the mud for you.
 
 ### Summary
 
@@ -191,27 +191,27 @@ Skills I use daily for code work.
 
 **User-invoked**
 
-- **[ask-matt](./skills/engineering/ask-matt/SKILL.md)** — Ask which skill or flow fits your situation. A router over the user-invoked skills in this repo.
-- **[grill-with-docs](./skills/engineering/grill-with-docs/SKILL.md)** — Grilling session that also builds your project's domain model, sharpening terminology and updating `CONTEXT.md` and ADRs inline.
-- **[triage](./skills/engineering/triage/SKILL.md)** — Move issues through a state machine of triage roles.
-- **[improve-codebase-architecture](./skills/engineering/improve-codebase-architecture/SKILL.md)** — Scan a codebase for deepening opportunities, present them as a visual HTML report, then grill through whichever one you pick.
-- **[setup-matt-pocock-skills](./skills/engineering/setup-matt-pocock-skills/SKILL.md)** — Configure this repo for the engineering skills (issue tracker, triage labels, domain doc layout). Run once per repo before using the other engineering skills.
-- **[to-spec](./skills/engineering/to-spec/SKILL.md)** — Turn the current conversation into a spec and publish it to the issue tracker. No interview — just synthesizes what you've already discussed.
-- **[to-tickets](./skills/engineering/to-tickets/SKILL.md)** — Break any plan, spec, or conversation into a set of tracer-bullet tickets, each declaring its blocking edges — written as text in a local file, or as native blocking links on a real tracker.
-- **[implement](./skills/engineering/implement/SKILL.md)** — Build the work described by a spec or set of tickets, driving `/tdd` at pre-agreed seams and closing out with `/code-review` before committing.
-- **[wayfinder](./skills/engineering/wayfinder/SKILL.md)** — Plan a huge chunk of work, more than one agent session can hold, as a shared map of decision tickets on the issue tracker — resolve them one at a time until the way to the destination is clear.
+- **[ask-matt](./skills/ask-matt/SKILL.md)** — Ask which skill or flow fits your situation. A router over the user-invoked skills in this repo.
+- **[grill-with-docs](./skills/grill-with-docs/SKILL.md)** — Grilling session that also builds your project's domain model, sharpening terminology and updating `CONTEXT.md` and ADRs inline.
+- **[triage](./skills/triage/SKILL.md)** — Move issues through a state machine of triage roles.
+- **[improve-codebase-architecture](./skills/improve-codebase-architecture/SKILL.md)** — Scan a codebase for deepening opportunities, present them as a visual HTML report, then grill through whichever one you pick.
+- **[setup-matt-pocock-skills](./skills/setup-matt-pocock-skills/SKILL.md)** — Configure this repo for the engineering skills (issue tracker, triage labels, domain doc layout). Run once per repo before using the other engineering skills.
+- **[to-spec](./skills/to-spec/SKILL.md)** — Turn the current conversation into a spec and publish it to the issue tracker. No interview — just synthesizes what you've already discussed.
+- **[to-tickets](./skills/to-tickets/SKILL.md)** — Break any plan, spec, or conversation into a set of tracer-bullet tickets, each declaring its blocking edges — written as text in a local file, or as native blocking links on a real tracker.
+- **[implement](./skills/implement/SKILL.md)** — Build the work described by a spec or set of tickets, driving `/tdd` at pre-agreed seams and closing out with `/code-review` before committing.
+- **[wayfinder](./skills/wayfinder/SKILL.md)** — Plan a huge chunk of work, more than one agent session can hold, as a shared map of decision tickets on the issue tracker — resolve them one at a time until the way to the destination is clear.
 
 **Model-invoked**
 
-- **[prototype](./skills/engineering/prototype/SKILL.md)** — Build a throwaway prototype to answer a design question — a single shareable HTML file for state/logic questions, or several radically different UI variations toggleable from one route.
-- **[diagnosing-bugs](./skills/engineering/diagnosing-bugs/SKILL.md)** — Disciplined diagnosis loop for hard bugs and performance regressions: build a feedback loop that goes red on this bug → minimise → hypothesise → instrument → fix → regression-test.
-- **[research](./skills/engineering/research/SKILL.md)** — Investigate a question against high-trust primary sources and capture the findings as a cited Markdown file in the repo, run as a background agent.
-- **[tdd](./skills/engineering/tdd/SKILL.md)** — Test-driven development with a red-green-refactor loop. Builds features or fixes bugs one vertical slice at a time.
-- **[domain-modeling](./skills/engineering/domain-modeling/SKILL.md)** — Actively build and sharpen a project's domain model — challenge terms against the glossary, stress-test with edge-case scenarios, and update `CONTEXT.md` and ADRs inline.
-- **[codebase-design](./skills/engineering/codebase-design/SKILL.md)** — Shared discipline and vocabulary for designing deep modules: a lot of behaviour behind a small interface, placed at a clean seam, testable through that interface.
-- **[code-review](./skills/engineering/code-review/SKILL.md)** — Two-axis review of the diff since a fixed point: **Standards** (does it follow the repo's coding standards, plus a Fowler smell baseline?) and **Spec** (does it faithfully implement the originating issue/spec?), run as parallel sub-agents so neither pollutes the other.
-- **[resolving-merge-conflicts](./skills/engineering/resolving-merge-conflicts/SKILL.md)** — Work through an in-progress git merge or rebase conflict hunk by hunk, resolving by intent traced to each side's primary source, then finish the operation — never `--abort`.
-- **[wizard](./skills/engineering/wizard/SKILL.md)** — Generate an interactive bash wizard that walks a human through steps only they can perform: provisioning infrastructure, setting up credentials or CI secrets, walking an unfamiliar third-party dashboard, or running a one-off migration or cutover.
+- **[prototype](./skills/prototype/SKILL.md)** — Build a throwaway prototype to answer a design question — a single shareable HTML file for state/logic questions, or several radically different UI variations toggleable from one route.
+- **[diagnosing-bugs](./skills/diagnosing-bugs/SKILL.md)** — Disciplined diagnosis loop for hard bugs and performance regressions: build a feedback loop that goes red on this bug → minimise → hypothesise → instrument → fix → regression-test.
+- **[research](./skills/research/SKILL.md)** — Investigate a question against high-trust primary sources and capture the findings as a cited Markdown file in the repo, run as a background agent.
+- **[tdd](./skills/tdd/SKILL.md)** — Test-driven development with a red-green-refactor loop. Builds features or fixes bugs one vertical slice at a time.
+- **[domain-modeling](./skills/domain-modeling/SKILL.md)** — Actively build and sharpen a project's domain model — challenge terms against the glossary, stress-test with edge-case scenarios, and update `CONTEXT.md` and ADRs inline.
+- **[codebase-design](./skills/codebase-design/SKILL.md)** — Shared discipline and vocabulary for designing deep modules: a lot of behaviour behind a small interface, placed at a clean seam, testable through that interface.
+- **[code-review](./skills/code-review/SKILL.md)** — Two-axis review of the diff since a fixed point: **Standards** (does it follow the repo's coding standards, plus a Fowler smell baseline?) and **Spec** (does it faithfully implement the originating issue/spec?), run as parallel sub-agents so neither pollutes the other.
+- **[resolving-merge-conflicts](./skills/resolving-merge-conflicts/SKILL.md)** — Work through an in-progress git merge or rebase conflict hunk by hunk, resolving by intent traced to each side's primary source, then finish the operation — never `--abort`.
+- **[wizard](./skills/wizard/SKILL.md)** — Generate an interactive bash wizard that walks a human through steps only they can perform: provisioning infrastructure, setting up credentials or CI secrets, walking an unfamiliar third-party dashboard, or running a one-off migration or cutover.
 
 ### Productivity
 
@@ -219,13 +219,13 @@ General workflow tools, not code-specific.
 
 **User-invoked**
 
-- **[grill-me](./skills/productivity/grill-me/SKILL.md)** — Get relentlessly interviewed about a plan or design until every branch of the design tree is resolved.
-- **[handoff](./skills/productivity/handoff/SKILL.md)** — Compact the current conversation into a handoff document so another agent can continue the work.
-- **[teach](./skills/productivity/teach/SKILL.md)** — Teach the user a new skill or concept over multiple sessions, using the current directory as a stateful teaching workspace.
-- **[to-questionnaire](./skills/productivity/to-questionnaire/SKILL.md)** — Turn a decision you can't answer alone into a Markdown questionnaire for the one person who can — filled in async, or together over a meeting. It grills you about the send (who it's for, what you need back), not the subject.
-- **[wait-what](./skills/productivity/wait-what/SKILL.md)** — Fire this the moment a message doesn't land. The agent re-pitches it with the context you're missing, in plain English, using your `CONTEXT.md` vocabulary.
+- **[grill-me](./skills/grill-me/SKILL.md)** — Get relentlessly interviewed about a plan or design until every branch of the design tree is resolved.
+- **[handoff](./skills/handoff/SKILL.md)** — Compact the current conversation into a handoff document so another agent can continue the work.
+- **[teach](./skills/teach/SKILL.md)** — Teach the user a new skill or concept over multiple sessions, using the current directory as a stateful teaching workspace.
+- **[to-questionnaire](./skills/to-questionnaire/SKILL.md)** — Turn a decision you can't answer alone into a Markdown questionnaire for the one person who can — filled in async, or together over a meeting. It grills you about the send (who it's for, what you need back), not the subject.
+- **[wait-what](./skills/wait-what/SKILL.md)** — Fire this the moment a message doesn't land. The agent re-pitches it with the context you're missing, in plain English, using your `CONTEXT.md` vocabulary.
 
 **Model-invoked**
 
-- **[grilling](./skills/productivity/grilling/SKILL.md)** — Interview the user relentlessly about a plan, decision, or idea until every branch of the design tree is resolved. The reusable interview primitive behind `grill-me`, `grill-with-docs`, `triage`, `wayfinder` and `improve-codebase-architecture`.
-- **[writing-for-agents](./skills/productivity/writing-for-agents/SKILL.md)** — Writing documents for agents: skills, AGENTS.md/CLAUDE.md, and any doc an agent reaches by a pointer.
+- **[grilling](./skills/grilling/SKILL.md)** — Interview the user relentlessly about a plan, decision, or idea until every branch of the design tree is resolved. The reusable interview primitive behind `grill-me`, `grill-with-docs`, `triage`, `wayfinder` and `improve-codebase-architecture`.
+- **[writing-for-agents](./skills/writing-for-agents/SKILL.md)** — Writing documents for agents: skills, AGENTS.md/CLAUDE.md, and any doc an agent reaches by a pointer.