test: add SettingsDialog integration tests and enhance MSW infrastructure

- Add comprehensive SettingsDialog integration tests with 3 test cases:
  * Load default settings from MSW
  * Import configuration and trigger success callback
  * Save settings and handle restart prompt
- Extend MSW handlers with settings-related endpoints:
  * get_settings/save_settings for settings management
  * app_config_dir_override for custom config directory
  * apply_claude_plugin_config for plugin integration
  * import/export config file operations
  * file/directory dialog mocks
- Add settings state management to MSW mock state:
  * Settings state with default values
  * appConfigDirOverride state
  * Reset logic in resetProviderState()
- Mock @tauri-apps/api/path for DirectorySettings tests
- Refactor App.test.tsx to focus on happy path scenarios:
  * Remove delete functionality test (covered in useProviderActions unit tests)
  * Reorganize test flow: settings → switch → usage → create → edit → switch → duplicate
  * Remove unnecessary state verifications
  * Simplify event testing

All tests passing: 4 integration tests + 12 unit tests

tests/msw/handlers.ts

@@ -1,6 +1,6 @@
 import { http, HttpResponse } from "msw";
 import type { AppType } from "@/lib/api/types";
-import type { Provider } from "@/types";
+import type { Provider, Settings } from "@/types";
 import {
   addProvider,
   deleteProvider,
@@ -11,6 +11,10 @@ import {
   setCurrentProviderId,
   updateProvider,
   updateSortOrder,
+  getSettings,
+  setSettings,
+  getAppConfigDirOverride,
+  setAppConfigDirOverrideState,
 } from "./state";
 
 const TAURI_ENDPOINT = "http://tauri.local";
@@ -97,4 +101,65 @@ export const handlers = [
   http.post(`${TAURI_ENDPOINT}/open_external`, () => success(true)),
 
   http.post(`${TAURI_ENDPOINT}/restart_app`, () => success(true)),
+
+  http.post(`${TAURI_ENDPOINT}/get_settings`, () => success(getSettings())),
+
+  http.post(`${TAURI_ENDPOINT}/save_settings`, async ({ request }) => {
+    const { settings } = await withJson<{ settings: Settings }>(request);
+    setSettings(settings);
+    return success(true);
+  }),
+
+  http.post(`${TAURI_ENDPOINT}/set_app_config_dir_override`, async ({ request }) => {
+    const { path } = await withJson<{ path: string | null }>(request);
+    setAppConfigDirOverrideState(path ?? null);
+    return success(true);
+  }),
+
+  http.post(`${TAURI_ENDPOINT}/get_app_config_dir_override`, () =>
+    success(getAppConfigDirOverride()),
+  ),
+
+  http.post(`${TAURI_ENDPOINT}/apply_claude_plugin_config`, async ({ request }) => {
+    const { official } = await withJson<{ official: boolean }>(request);
+    setSettings({ enableClaudePluginIntegration: !official });
+    return success(true);
+  }),
+
+  http.post(`${TAURI_ENDPOINT}/get_config_dir`, async ({ request }) => {
+    const { app_type } = await withJson<{ app_type: AppType }>(request);
+    return success(app_type === "claude" ? "/default/claude" : "/default/codex");
+  }),
+
+  http.post(`${TAURI_ENDPOINT}/is_portable_mode`, () => success(false)),
+
+  http.post(`${TAURI_ENDPOINT}/select_config_directory`, async ({ request }) => {
+    const { default_path } = await withJson<{ default_path?: string }>(request);
+    return success(default_path ? `${default_path}/picked` : "/mock/selected-dir");
+  }),
+
+  http.post(`${TAURI_ENDPOINT}/open_file_dialog`, () =>
+    success("/mock/import-settings.json"),
+  ),
+
+  http.post(`${TAURI_ENDPOINT}/import_config_from_file`, async ({ request }) => {
+    const { filePath } = await withJson<{ filePath: string }>(request);
+    if (!filePath) {
+      return success({ success: false, message: "Missing file" });
+    }
+    setSettings({ language: "en" });
+    return success({ success: true, backupId: "backup-123" });
+  }),
+
+  http.post(`${TAURI_ENDPOINT}/export_config_to_file`, async ({ request }) => {
+    const { filePath } = await withJson<{ filePath: string }>(request);
+    if (!filePath) {
+      return success({ success: false, message: "Invalid destination" });
+    }
+    return success({ success: true, filePath });
+  }),
+
+  http.post(`${TAURI_ENDPOINT}/save_file_dialog`, () =>
+    success("/mock/export-settings.json"),
+  ),
 ];