chore: set up changesets

Add changesets for tracking and versioning skill changes:
- package.json (private) + @changesets/cli and @changesets/changelog-github
- .changeset/config.json using the GitHub release-style changelog
- release workflow that opens a version PR on push to main (no npm publish)
- initial changeset recording recent skill updates

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.changeset/README.md

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+# Changesets
+
+Hello and welcome! This folder has been automatically generated by `@changesets/cli`, a build tool that works
+with multi-package repos, or single-package repos to help you version and publish your code. You can
+find the full documentation for it [in our repository](https://github.com/changesets/changesets).
+
+We have a quick list of common questions to get you started engaging with this project in
+[our documentation](https://github.com/changesets/changesets/blob/main/docs/common-questions.md).

.changeset/config.json

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+{
+  "$schema": "https://unpkg.com/@changesets/config@3.1.4/schema.json",
+  "changelog": [
+    "@changesets/changelog-github",
+    { "repo": "mattpocock/skills" }
+  ],
+  "commit": false,
+  "fixed": [],
+  "linked": [],
+  "access": "restricted",
+  "baseBranch": "main",
+  "updateInternalDependencies": "patch",
+  "ignore": []
+}

.changeset/initial-skill-updates.md

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+---
+"mattpocock-skills": minor
+---
+
+Recent skill updates:
+
+- Add `ask-matt` user-invoked skill for triage and multi-session build guidance.
+- Add `writing-great-skills` skill, with no-op hunting at the sentence level.
+- Add `decision-mapping`, `prefactoring`, and `implement` (PRD-based) skills.
+- Tighten the review skill: fail-fast ref check, single-sourced rules, no-op cuts.
+- Rename terminology from Commands/Skills to User-invoked/Model-invoked across the docs.
+- Remove the `caveman` and `zoom-out` skills and all references.