feat: add comprehensive Playwright testing suite with visual regression

- Add Playwright configuration with multi-browser testing
- Create basic functionality tests for game mechanics
- Add gameplay tests with keyboard and touch interactions
- Implement visual regression testing with screenshots
- Add environment-specific tests for dev/staging/prod
- Include health endpoint and security header validation
- Set up test infrastructure for CI/CD pipeline

tests/package.json

@@ -0,0 +1,14 @@
+{
+  "name": "playwright-tests",
+  "version": "1.0.0",
+  "description": "Playwright tests for 2048 game",
+  "scripts": {
+    "test": "playwright test",
+    "test:headed": "playwright test --headed",
+    "test:debug": "playwright test --debug",
+    "test:ui": "playwright test --ui"
+  },
+  "devDependencies": {
+    "@playwright/test": "^1.40.0"
+  }
+}