Phase 5.4-5.11: Playwright E2E test infrastructure with 7 spec files

- playwright.config.ts: chromium project, webServer, baseURL, trace/screenshot/video
- e2e/helpers.ts: API mock setup, login/logout helpers, mock data for all entities
- 7 E2E spec files (1164 lines total):
  - auth.spec.ts: login/logout workflow
  - contact-crud.spec.ts: create/edit/delete contacts, add persons
  - search.spec.ts: global search, filter, results
  - plugin-toggle.spec.ts: enable/disable plugins, UI changes
  - mail.spec.ts: mail account setup, folders, mail viewing
  - dms.spec.ts: folder creation, file upload, preview, share
  - calendar.spec.ts: appointment creation, calendar switch, kanban view
- @playwright/test added as devDependency
- e2e scripts added to package.json
- TSC: 0 new errors (only pre-existing Dms.tsx)

frontend/package.json

@@ -9,7 +9,10 @@
     "preview": "vite preview",
     "test": "vitest run src/__tests__/ --reporter=verbose",
     "test:coverage": "vitest run src/__tests__/ --coverage",
-    "typecheck": "tsc --noEmit"
+    "typecheck": "tsc --noEmit",
+    "e2e": "playwright test",
+    "e2e:ui": "playwright test --ui",
+    "e2e:headed": "playwright test --headed"
   },
   "dependencies": {
     "@hookform/resolvers": "^3.9.0",
@@ -58,6 +61,7 @@
     "typescript": "^5.6.0",
     "vite": "^5.4.0",
     "vite-bundle-visualizer": "^1.2.1",
-    "vitest": "^2.1.0"
+    "vitest": "^2.1.0",
+    "@playwright/test": "^1.48.0"
   }
 }