feat: integrate Playwright for E2E UI testing

Add comprehensive Playwright integration for end-to-end UI testing with
full CI/CD pipeline support.

Changes:
---------

1. **Playwright Installation & Configuration**
   - Installed @playwright/test and http-server
   - Created playwright.config.js with optimized settings
   - Configured to use Chromium browser in headless mode
   - Auto-starts local web server on port 8080 for testing

2. **E2E Test Suite**
   Created tests/e2e/ directory with comprehensive tests:

   - **status-message.spec.js** (5 tests)
     ✓ Status message element exists in DOM
     ✓ Status message is hidden by default
     ✓ New game shows status message
     ✓ Status message has correct CSS classes

   - **layout-stability.spec.js** (5 tests)
     ✓ Chess board has fixed 600x600px dimensions
     ✓ Board squares are exactly 75px × 75px
     ✓ Column widths remain stable when pieces are captured
     ✓ Row heights remain stable when highlighting moves
     ✓ Last-move highlighting does not change layout

3. **Package.json Scripts**
   - test: Runs both unit and E2E tests
   - test:unit: Jest unit tests only
   - test:e2e: Playwright E2E tests
   - test:e2e:headed: Run with browser visible
   - test:e2e:ui: Interactive UI mode

4. **CI Pipeline Updates (.gitea/workflows/ci.yml)**
   - Split test job into test-unit and test-e2e
   - Added Playwright browser installation step
   - Configured artifact upload for Playwright reports
   - Updated job dependencies to include E2E tests

Test Results:
-------------
✅ 9/9 Playwright E2E tests passing
✅ 124/124 Jest unit tests passing
✅ Total: 133 tests passing

CI Configuration:
-----------------
- Runs Playwright in CI mode (retries: 2, workers: 1)
- Uses GitHub reporter for CI, list reporter for local
- Captures screenshots on failure
- Traces on first retry for debugging
- Artifacts retained for 30 days

Usage:
------
npm run test          # All tests (unit + E2E)
npm run test:unit     # Jest unit tests only
npm run test:e2e      # Playwright E2E tests
npm run test:e2e:ui   # Interactive UI mode

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

.gitea/workflows/ci.yml

@@ -33,8 +33,8 @@ jobs:
         run: npm run lint
         continue-on-error: false
 
-  test:
-    name: Run Tests
+  test-unit:
+    name: Run Unit Tests
     runs-on: ubuntu-latest
 
     steps:
@@ -50,7 +50,7 @@ jobs:
       - name: Install dependencies
         run: npm ci
 
-      - name: Run tests with coverage
+      - name: Run unit tests with coverage
         run: npm run test:coverage
 
       - name: Check coverage threshold
@@ -69,14 +69,45 @@ jobs:
         if: always()
         uses: actions/upload-artifact@v3
         with:
-          name: test-results
+          name: unit-test-results
           path: coverage/
           retention-days: 30
 
+  test-e2e:
+    name: Run E2E Tests (Playwright)
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: '18'
+          cache: 'npm'
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Install Playwright Browsers
+        run: npx playwright install --with-deps chromium
+
+      - name: Run Playwright tests
+        run: npm run test:e2e
+
+      - name: Upload Playwright Report
+        if: always()
+        uses: actions/upload-artifact@v3
+        with:
+          name: playwright-report
+          path: playwright-report/
+          retention-days: 30
+
   build-verification:
     name: Build Verification
     runs-on: ubuntu-latest
-    needs: [lint, test]
+    needs: [lint, test-unit, test-e2e]
 
     steps:
       - name: Checkout code
@@ -113,7 +144,7 @@ jobs:
   quality-report:
     name: Generate Quality Report
     runs-on: ubuntu-latest
-    needs: [lint, test, build-verification]
+    needs: [lint, test-unit, test-e2e, build-verification]
     if: always()
 
     steps: