misc: demote to a non-promoted bucket

misc/ skills are no longer installable via the plugin or listed in the
top-level README — they join personal/ as kept-but-unshipped. Only
engineering/ and productivity/ are promoted now.

- Drop the Misc section from the top-level README.
- Reclassify misc/ as non-promoted in CLAUDE.md (README/plugin rule,
  bucket-README grouping rule, docs-page rule) and the writing-docs guide.
- Note the non-promoted status in the misc bucket README.

plugin.json already omitted misc, so no manifest change was needed.
No SKILL.md context pointer referenced a misc skill, so nothing else
had to move.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

README.md

@@ -179,12 +179,3 @@ General workflow tools, not code-specific.
 **Model-invoked**
 
 - **[grilling](./skills/productivity/grilling/SKILL.md)** — Interview the user relentlessly about a plan or design until every branch of the decision tree is resolved. The reusable loop behind `grill-me` and `grill-with-docs`.
-
-### Misc
-
-Tools I keep around but rarely use.
-
-- **[git-guardrails-claude-code](./skills/misc/git-guardrails-claude-code/SKILL.md)** — Set up Claude Code hooks to block dangerous git commands (push, reset --hard, clean, etc.) before they execute.
-- **[migrate-to-shoehorn](./skills/misc/migrate-to-shoehorn/SKILL.md)** — Migrate test files from `as` type assertions to @total-typescript/shoehorn.
-- **[scaffold-exercises](./skills/misc/scaffold-exercises/SKILL.md)** — Create exercise directory structures with sections, problems, solutions, and explainers.
-- **[setup-pre-commit](./skills/misc/setup-pre-commit/SKILL.md)** — Set up Husky pre-commit hooks with lint-staged, Prettier, type checking, and tests.