Add GitHub Actions workflow with artifact attestation for releases

- Create build job that compiles main.js and styles.css
- Add attest job using actions/attest-build-provenance for both assets
- Create release job that publishes artifacts with their attestations
- Enables users to cryptographically verify release asset provenance

.github/workflows/release.yml

@@ -0,0 +1,82 @@
+name: Release
+
+on:
+  push:
+    tags:
+      - '*'
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+    outputs:
+      main-js-path: ${{ steps.build.outputs.main-js-path }}
+      styles-css-path: ${{ steps.build.outputs.styles-css-path }}
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: '20'
+          cache: 'npm'
+
+      - run: npm ci
+      - run: npm run build
+
+      - id: build
+        run: |
+          echo "main-js-path=main.js" >> $GITHUB_OUTPUT
+          echo "styles-css-path=styles.css" >> $GITHUB_OUTPUT
+
+  attest:
+    needs: build
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      id-token: write
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: '20'
+          cache: 'npm'
+
+      - run: npm ci
+      - run: npm run build
+
+      - name: Attest build provenance for main.js
+        uses: actions/attest-build-provenance@v1
+        with:
+          subject-path: main.js
+
+      - name: Attest build provenance for styles.css
+        uses: actions/attest-build-provenance@v1
+        with:
+          subject-path: styles.css
+
+  release:
+    needs: [build, attest]
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+      id-token: write
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: '20'
+          cache: 'npm'
+
+      - run: npm ci
+      - run: npm run build
+
+      - name: Create Release
+        uses: softprops/action-gh-release@v1
+        with:
+          files: |
+            main.js
+            styles.css
+            manifest.json