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

tests/msw/tauriMocks.ts

@@ -0,0 +1,61 @@
+import "cross-fetch/polyfill";
+import { vi } from "vitest";
+import { server } from "./server";
+
+const TAURI_ENDPOINT = "http://tauri.local";
+
+vi.mock("@tauri-apps/api/core", () => ({
+  invoke: async (command: string, payload: Record<string, unknown> = {}) => {
+    const response = await fetch(`${TAURI_ENDPOINT}/${command}`, {
+      method: "POST",
+      headers: {
+        "Content-Type": "application/json",
+      },
+      body: JSON.stringify(payload ?? {}),
+    });
+
+    if (!response.ok) {
+      const text = await response.text();
+      throw new Error(text || `Invoke failed for ${command}`);
+    }
+
+    const text = await response.text();
+    if (!text) return undefined;
+    try {
+      return JSON.parse(text);
+    } catch {
+      return text;
+    }
+  },
+}));
+
+const listeners = new Map<
+  string,
+  Set<(event: { payload: unknown }) => void>
+>();
+
+const ensureListenerSet = (event: string) => {
+  if (!listeners.has(event)) {
+    listeners.set(event, new Set());
+  }
+  return listeners.get(event)!;
+};
+
+export const emitTauriEvent = (event: string, payload: unknown) => {
+  const handlers = listeners.get(event);
+  handlers?.forEach((handler) => handler({ payload }));
+};
+
+vi.mock("@tauri-apps/api/event", () => ({
+  listen: async (event: string, handler: (event: { payload: unknown }) => void) => {
+    const set = ensureListenerSet(event);
+    set.add(handler);
+    return () => {
+      set.delete(handler);
+    };
+  },
+}));
+
+// Ensure the MSW server is referenced so tree shaking doesn't remove imports
+void server;
+