feat: add GitHub Actions release workflow

Implements automated release workflow per design document.

- Triggers on semantic version tags (e.g., 1.2.3)
- Validates version consistency across package.json, manifest.json, and git tag
- Runs test suite (blocks release if tests fail)
- Builds plugin using production build process
- Verifies build artifacts exist (main.js, manifest.json, styles.css)
- Creates draft GitHub release with required files

Workflow uses single-job architecture for simplicity and runs on Node.js 18 with npm caching for performance.

.github/workflows/release.yml

@@ -0,0 +1,91 @@
+name: Release Plugin
+
+on:
+  push:
+    tags:
+      - "[0-9]+.[0-9]+.[0-9]+"
+
+jobs:
+  release:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Validate version consistency
+        run: |
+          TAG_VERSION="${GITHUB_REF#refs/tags/}"
+          PKG_VERSION=$(node -p "require('./package.json').version")
+          MANIFEST_VERSION=$(node -p "require('./manifest.json').version")
+
+          echo "Checking version consistency..."
+          echo "Git tag: $TAG_VERSION"
+          echo "package.json: $PKG_VERSION"
+          echo "manifest.json: $MANIFEST_VERSION"
+
+          if [ "$TAG_VERSION" != "$PKG_VERSION" ] || [ "$TAG_VERSION" != "$MANIFEST_VERSION" ]; then
+            echo "❌ Version mismatch detected!"
+            echo "Git tag: $TAG_VERSION"
+            echo "package.json: $PKG_VERSION"
+            echo "manifest.json: $MANIFEST_VERSION"
+            exit 1
+          fi
+
+          echo "✅ All versions match: $TAG_VERSION"
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: '18'
+          cache: 'npm'
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Run tests
+        run: npm test
+
+      - name: Build plugin
+        run: npm run build
+
+      - name: Verify build artifacts
+        run: |
+          echo "Verifying required files exist..."
+
+          if [ ! -f main.js ]; then
+            echo "❌ main.js not found!"
+            exit 1
+          fi
+
+          if [ ! -f manifest.json ]; then
+            echo "❌ manifest.json not found!"
+            exit 1
+          fi
+
+          if [ ! -f styles.css ]; then
+            echo "❌ styles.css not found!"
+            exit 1
+          fi
+
+          echo "✅ All required files present"
+          echo "File sizes:"
+          ls -lh main.js manifest.json styles.css
+
+      - name: Create draft release
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          TAG_VERSION="${GITHUB_REF#refs/tags/}"
+
+          gh release create "$TAG_VERSION" \
+            --title="$TAG_VERSION" \
+            --draft \
+            main.js \
+            manifest.json \
+            styles.css
+
+          echo "✅ Draft release created: $TAG_VERSION"
+          echo "Visit https://github.com/${{ github.repository }}/releases to review and publish"