test: migrate to MSW testing architecture for App integration test

Major testing infrastructure upgrade from manual mocks to Mock Service Worker (MSW):

New MSW infrastructure (tests/msw/):
- Add state.ts: In-memory state manager with full CRUD operations
  - Manage providers and current selections per app type (Claude/Codex)
  - Auto-switch current provider when deleted
  - Deep clone to prevent reference pollution
- Add handlers.ts: HTTP request handlers for 10 Tauri API endpoints
  - Mock get_providers, switch_provider, add/update/delete_provider
  - Mock update_sort_order, update_tray_menu, import_default_config
  - Support error scenarios (404 for non-existent providers)
- Add tauriMocks.ts: Tauri API mock layer
  - Transparently convert invoke() calls to HTTP requests
  - Mock event listener system with emitTauriEvent helper
  - Use cross-fetch for Node.js environment
- Add server.ts: MSW server setup for Node.js test environment

Refactor App.test.tsx (-170 lines, -43%):
- Remove 23 manual mocks (useProvidersQuery, useProviderActions, etc.)
- Run real hooks with MSW-backed API calls instead of mock implementations
- Test real state changes instead of mock call counts
- Add comprehensive flow: duplicate → create → edit → delete → event listening
- Verify actual provider list changes and current selection updates

Setup integration:
- Add MSW server lifecycle to tests/setupTests.ts
  - Start server before all tests
  - Reset handlers and state after each test
  - Close server after all tests complete
- Clear all mocks in afterEach for test isolation

Dependencies:
- Add msw@^2.11.6 for API mocking
- Add cross-fetch@^4.1.0 for fetch polyfill in Node.js

Type fixes:
- Add missing imports (AppType, Provider) in handlers.ts
- Fix HttpResponse.json generic constraint with as any (MSW best practice)
- Change invalid category "default" to "official" in state.ts

Test results: All 50 tests passing across 8 files, 0 TypeScript errors

package.json

@@ -19,14 +19,16 @@
   "license": "MIT",
   "devDependencies": {
     "@tauri-apps/cli": "^2.8.0",
+    "@testing-library/jest-dom": "^6.6.3",
+    "@testing-library/react": "^16.0.1",
+    "@testing-library/user-event": "^14.5.2",
     "@types/node": "^20.0.0",
     "@types/react": "^18.2.0",
     "@types/react-dom": "^18.2.0",
     "@vitejs/plugin-react": "^4.2.0",
-    "@testing-library/jest-dom": "^6.6.3",
-    "@testing-library/react": "^16.0.1",
-    "@testing-library/user-event": "^14.5.2",
+    "cross-fetch": "^4.1.0",
     "jsdom": "^25.0.0",
+    "msw": "^2.11.6",
     "prettier": "^3.6.2",
     "typescript": "^5.3.0",
     "vite": "^5.0.0",