feat: graduate to-questionnaire into the productivity bucket

Move `to-questionnaire` out of in-progress into `productivity/` and wire
it up as a promoted skill: plugin.json entry, top-level + Productivity
READMEs under User-invoked, a docs page at
docs/productivity/to-questionnaire.md, and a Standalone route in
ask-matt framing it as the inverse of /grill-me.

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

README.md

@@ -206,6 +206,7 @@ General workflow tools, not code-specific.
 - **[grill-me](./skills/productivity/grill-me/SKILL.md)** — Get relentlessly interviewed about a plan or design until every branch of the decision 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.
 - **[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.
 
 **Model-invoked**