ci: add GitHub Actions CI + release workflow

CI:
- Tests on Node 18, 20, 22
- Runs on push to main and PRs

Release (triggered by v* tags):
- Runs tests first
- Publishes to npm with provenance
- Creates GitHub Release with auto-generated notes

Usage: git tag v0.1.0 && git push --tags

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: patricker

.github/workflows/ci.yml

@@ -0,0 +1,27 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  test:
+    name: Test (Node ${{ matrix.node-version }})
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        node-version: [18, 20, 22]
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: ${{ matrix.node-version }}
+
+      - name: Install
+        run: npm ci
+
+      - name: Test
+        run: npm test

.github/workflows/release.yml

@@ -0,0 +1,68 @@
+name: Release
+
+on:
+  push:
+    tags: ["v*"]
+
+permissions:
+  contents: write
+  id-token: write
+
+jobs:
+  test:
+    name: Test
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 20
+
+      - run: npm ci
+      - run: npm test
+
+  publish-npm:
+    name: Publish to npm
+    needs: test
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 20
+          registry-url: https://registry.npmjs.org
+
+      - run: npm ci
+      - run: npm publish --provenance --access public
+        env:
+          NODE_AUTH_TOKEN: ${{ secrets.NPM_TOKEN }}
+
+  github-release:
+    name: GitHub Release
+    needs: test
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Generate release notes
+        id: notes
+        run: |
+          # Get the previous tag
+          PREV_TAG=$(git tag --sort=-v:refname | head -2 | tail -1)
+          if [ -z "$PREV_TAG" ]; then
+            echo "body=Initial release" >> $GITHUB_OUTPUT
+          else
+            NOTES=$(git log ${PREV_TAG}..HEAD --pretty=format:"- %s" --no-merges)
+            echo "body<<EOF" >> $GITHUB_OUTPUT
+            echo "$NOTES" >> $GITHUB_OUTPUT
+            echo "EOF" >> $GITHUB_OUTPUT
+          fi
+
+      - uses: softprops/action-gh-release@v2
+        with:
+          body: ${{ steps.notes.outputs.body }}
+          generate_release_notes: true