Add CI workflow

.github/workflows/ci.yml

@@ -0,0 +1,43 @@
+name: CI
+
+on:
+  pull_request:
+    branches: [main]
+  push:
+    branches: [main]
+
+jobs:
+  validate:
+    name: Validate PR
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Install pnpm
+        uses: pnpm/action-setup@v4
+        with:
+          version: 9
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: 'lts/*'
+          cache: 'pnpm'
+
+      - name: Install dependencies
+        run: pnpm install --frozen-lockfile
+
+      - name: Type check
+        run: pnpm compile
+
+      - name: Build extension
+        run: pnpm build
+
+      - name: Upload build artifacts
+        uses: actions/upload-artifact@v4
+        with:
+          name: chrome-extension
+          path: .output/chrome-mv3
+          retention-days: 7