feat: add update-changelog project skill

.claude/skills/update-changelog.md

@@ -0,0 +1,54 @@
+# update-changelog
+
+Use this skill when a feature has shipped, a bug has been fixed, or a feature has been removed. It updates CHANGELOG.md with a new versioned entry.
+
+## Process
+
+1. Read `CHANGELOG.md` — find the current latest version number (top `## [x.y.z]` entry)
+
+2. Check recent git history for context on what changed:
+   ```bash
+   git log --oneline -20
+   ```
+
+3. Read `docs/ROADMAP.md` — check what moved to Completed since the last changelog entry
+
+4. Determine the version bump:
+   - **Patch** (0.1.x → 0.1.x+1): bug fixes, minor UI polish, no new user-facing features
+   - **Minor** (0.x.0 → 0.x+1.0): new features or meaningful enhancements
+   - **Major** (x.0.0 → x+1.0.0): breaking changes or significant redesigns (rare)
+
+5. Write a new entry **above** the previous version, using today's date and the bumped version:
+
+   ```markdown
+   ## [0.2.0] - YYYY-MM-DD
+
+   ### Added
+   - Feature name — brief description of what it does for users
+
+   ### Changed
+   - What changed and why
+
+   ### Fixed
+   - Bug description — what was wrong and what's right now
+
+   ### Removed
+   - What was removed and why
+   ```
+
+   Only include sections that apply. Skip empty sections.
+
+6. Update `docs/HANDBOOK.md` if the change affects feature descriptions or known limitations (use the `update-handbook` skill or do it inline).
+
+7. Commit:
+   ```bash
+   git add CHANGELOG.md
+   git commit -m "chore: changelog v0.x.y"
+   ```
+
+## Versioning rules
+
+- Write entries for users, not developers ("Added initiative tracker" not "Added registerInitiativeHandlers to socket.ts")
+- One entry per version bump — don't create multiple entries for the same version
+- The `[Unreleased]` section at the top is for changes not yet assigned a version; move them down when cutting a release
+- Keep descriptions brief but specific — "Fixed HP leak exposing enemy stats to players" beats "Fixed bug"