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

.gitignore

@@ -9,6 +9,7 @@ Thumbs.db
 
 # Claude Code (machine-local)
 .claude/settings.local.json
+.mcp.json
 .rodney/
 .agent-tests/