test: add E2E tests covering full user journeys

- Create tests/e2e/full-flow.spec.ts with 5 E2E scenarios
- Test home page navigation and layout
- Test game creation via form
- Test metadata search functionality
- Test ROM-to-game linking workflow
- Test complete user journey: create → search → link → view
- Configure Playwright for multi-browser testing (chromium, firefox, webkit)
- Optimize playwright.config.ts for E2E stability
- Total: 15 tests (5 scenarios × 3 browsers)

package.json

@@ -15,6 +15,8 @@
     "test:install": "playwright install --with-deps",
     "test:ci": "vitest run --reporter=github",
     "test:playwright": "playwright test",
+    "test:e2e": "playwright test tests/e2e",
+    "test:e2e:debug": "playwright test tests/e2e --debug",
     "lint": "eslint . --ext .js,.ts",
     "format": "prettier --write .",
     "start": "node src/index.js"