Add Playwright E2E tests with MSW API mocking

- Playwright + @msw/playwright + @msw/source for OpenAPI-driven mocks
- Chromium-only configuration with Vite dev server integration
- Smoke tests: home page, CTA, navigation
- US-1 tests: validation, event creation flow, localStorage, error handling
- Suppress Node 25 --localstorage-file warning from MSW cookieStore

frontend/package.json

@@ -14,7 +14,10 @@
     "lint": "run-s lint:*",
     "lint:oxlint": "oxlint . --fix",
     "lint:eslint": "eslint . --fix --cache",
-    "format": "prettier --write --experimental-cli src/"
+    "format": "prettier --write --experimental-cli src/",
+    "test:e2e": "playwright test",
+    "test:e2e:ui": "playwright test --ui",
+    "test:e2e:debug": "playwright test --debug"
   },
   "dependencies": {
     "openapi-fetch": "^0.17.0",
@@ -22,6 +25,9 @@
     "vue-router": "^5.0.3"
   },
   "devDependencies": {
+    "@msw/playwright": "^0.6.5",
+    "@msw/source": "^0.6.1",
+    "@playwright/test": "^1.58.2",
     "@tsconfig/node24": "^24.0.4",
     "@types/jsdom": "^28.0.0",
     "@types/node": "^24.11.0",
@@ -36,6 +42,7 @@
     "eslint-plugin-vue": "~10.8.0",
     "jiti": "^2.6.1",
     "jsdom": "^28.1.0",
+    "msw": "^2.12.10",
     "npm-run-all2": "^8.0.4",
     "openapi-typescript": "^7.13.0",
     "oxlint": "~1.50.0",