Make CI fail if there are unformatted changes.

Fixes https://b.corp.google.com/issues/411720532

.github/workflows/ci.yml

@@ -21,7 +21,7 @@ jobs:
     steps:
       # 1. Checkout Code
       - name: Checkout repository
-        uses: actions/checkout@v4 
+        uses: actions/checkout@v4
 
       # 2. Setup Node.js Environment
       - name: Set up Node.js ${{ matrix.node-version }}
@@ -35,23 +35,29 @@ jobs:
       - name: Install dependencies
         run: npm ci
 
-      # 4. Linting
+      # 4. Check Formatting
+      - name: Run formatter check
+        run: |
+          npm run format
+          git diff --exit-code
+
+      # 5. Linting
       - name: Run linter
         run: npm run lint
         continue-on-error: true # TODO: Remove this when we have fixed lint errors
 
-      # 5. Type Checking
+      # 6. Type Checking
       - name: Run type check
         run: npm run typecheck # Or: tsc --noEmit
         continue-on-error: true # TODO: Remove this when we have fixed type errors
 
-      # 6. Build
+      # 7. Build
       # Optional if your tests run directly on TS files (e.g., using ts-jest, ts-node)
       # But usually good practice to ensure the build itself works.
       - name: Build project
         run: npm run build
 
-      # 7. Testing 
+      # 8. Testing
       # Uncomment when we have tests.
       #- name: Run tests
       #  run: npm test