docs: remove the source link from every skills page

Every docs page opened with a [Source](github.com/...) link, and
.agents/writing-docs.md told agents to add one to each new page.
Remove the line from all 25 pages, rewrite the one inline use in
ask-matt.md, and drop the rule from the page template, the fixed
frame list, and the "Done when" list so the links do not come back.

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

.agents/writing-docs.md

@@ -12,14 +12,12 @@ There is no H1 — the published page takes its title from the slug.
 
 ## Page structure
 
-Fill the template below. The **fixed frame** (source link, `## What it does`, `## When to reach for it`, `## Where it fits`) appears on every page. The **adaptable middle** — `## Prerequisites` and the free-form substance sections — carries only what this particular skill earns; delete the rest.
+Fill the template below. The **fixed frame** (`## What it does`, `## When to reach for it`, `## Where it fits`) appears on every page. The **adaptable middle** — `## Prerequisites` and the free-form substance sections — carries only what this particular skill earns; delete the rest.
 
 **A page carries no install commands.** The ai-hero page template renders the install widget itself — a copy button, the single-skill command, the whole-set command, and the update line — above the body. A page that also writes them out shows the reader the same command twice, and the two copies drift: the hand-written pair on every page went stale against the widget beside it. Install wording is a property of the site, not of the page. If it needs changing, change it in ai-hero; the canonical wording lives in [the install block](./install-block.md).
 
 <page-template>
 
-[Source](https://github.com/mattpocock/skills/tree/main/skills/<bucket>/<name>)
-
 ## What it does
 
 One or two plain-language paragraphs. Lead with the skill's one-sentence job, then state the **defining constraint** — the single fact that makes this skill behave differently from the obvious default (for `to-spec`: it does not interview the user again, it synthesises what is already known). Write it as a plain declarative sentence — never a labelled aside like "The defining constraint:" or "The key thing:"; the formula reads as filler. This line is the most valuable on the page; never omit it.
@@ -64,7 +62,7 @@ Always present. Situate the skill in the system in a sentence or two:
 ## Done when
 
 - The page exists at `docs/<bucket>/<name>.md`, and no stale page survives a rename or bucket move.
-- The source link names the correct bucket and skill, and the page writes no install command of its own.
+- The page carries no source link and writes no install command of its own.
 - `## What it does` states the defining constraint, as plain prose rather than a labelled aside.
 - `## When to reach for it` states invocation mode and the trigger boundary.
 - `## Where it fits` names the role and links to `ask-matt`.