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>

.github/workflows/release.yml

@@ -0,0 +1,36 @@
+name: Release
+
+on:
+  push:
+    branches:
+      - main
+
+concurrency: ${{ github.workflow }}-${{ github.ref }}
+
+jobs:
+  release:
+    name: Version
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+      pull-requests: write
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: 22
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Create Version Pull Request
+        uses: changesets/action@v1
+        with:
+          version: npx changeset version
+          commit: "chore: version skills"
+          title: "chore: version skills"
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}