feat: complete stage 4 cleanup and code formatting

This commit completes stage 4 of the refactoring plan, focusing on cleanup
and optimization of the modernized codebase.

## Key Changes

### Code Cleanup
- Remove legacy `src/lib/styles.ts` (no longer needed)
- Remove old modal components (`ImportProgressModal.tsx`, `ProviderList.tsx`)
- Streamline `src/lib/tauri-api.ts` from 712 lines to 17 lines (-97.6%)
  - Remove global `window.api` pollution
  - Keep only event listeners (`tauriEvents.onProviderSwitched`)
  - All API calls now use modular `@/lib/api/*` layer

### Type System
- Clean up `src/vite-env.d.ts` (remove 156 lines of outdated types)
- Remove obsolete global type declarations
- All TypeScript checks pass with zero errors

### Code Formatting
- Format all source files with Prettier (82 files)
- Fix formatting issues in 15 files:
  - App.tsx and core components
  - MCP management components
  - Settings module components
  - Provider management components
  - UI components

### Documentation Updates
- Update `REFACTORING_CHECKLIST.md` with stage 4 progress
- Mark completed tasks in `REFACTORING_MASTER_PLAN.md`

## Impact

**Code Reduction:**
- Total: -1,753 lines, +384 lines (net -1,369 lines)
- tauri-api.ts: 712 → 17 lines (-97.6%)
- Removed styles.ts: -82 lines
- Removed vite-env.d.ts declarations: -156 lines

**Quality Improvements:**
- ✅ Zero TypeScript errors
- ✅ Zero TODO/FIXME comments
- ✅ 100% Prettier compliant
- ✅ Zero `window.api` references
- ✅ Fully modular API layer

## Testing
- [x] TypeScript compilation passes
- [x] Code formatting validated
- [x] No linting errors

Stage 4 completion: 100%
Ready for stage 5 (testing and bug fixes)

src/hooks/useSettings.ts

@@ -62,12 +62,17 @@ const computeDefaultAppConfigDir = async (): Promise<string | undefined> => {
     const home = await homeDir();
     return await join(home, ".cc-switch");
   } catch (error) {
-    console.error("[useSettings] Failed to resolve default app config dir", error);
+    console.error(
+      "[useSettings] Failed to resolve default app config dir",
+      error,
+    );
     return undefined;
   }
 };
 
-const computeDefaultConfigDir = async (app: AppType): Promise<string | undefined> => {
+const computeDefaultConfigDir = async (
+  app: AppType,
+): Promise<string | undefined> => {
   try {
     const home = await homeDir();
     const folder = app === "claude" ? ".claude" : ".codex";
@@ -83,8 +88,12 @@ export function useSettings(): UseSettingsResult {
   const { data, isLoading } = useSettingsQuery();
   const saveMutation = useSaveSettingsMutation();
 
-  const [settingsState, setSettingsState] = useState<SettingsFormState | null>(null);
-  const [appConfigDir, setAppConfigDir] = useState<string | undefined>(undefined);
+  const [settingsState, setSettingsState] = useState<SettingsFormState | null>(
+    null,
+  );
+  const [appConfigDir, setAppConfigDir] = useState<string | undefined>(
+    undefined,
+  );
   const [configPath, setConfigPath] = useState("");
   const [isPortable, setIsPortable] = useState(false);
   const [requiresRestart, setRequiresRestart] = useState(false);
@@ -135,7 +144,8 @@ export function useSettings(): UseSettingsResult {
       ...data,
       showInTray: data.showInTray ?? true,
       minimizeToTrayOnClose: data.minimizeToTrayOnClose ?? true,
-      enableClaudePluginIntegration: data.enableClaudePluginIntegration ?? false,
+      enableClaudePluginIntegration:
+        data.enableClaudePluginIntegration ?? false,
       claudeConfigDir: sanitizeDir(data.claudeConfigDir),
       codexConfigDir: sanitizeDir(data.codexConfigDir),
       language: normalizedLanguage,
@@ -286,8 +296,8 @@ export function useSettings(): UseSettingsResult {
       const key: DirectoryKey = app === "claude" ? "claude" : "codex";
       const currentValue =
         key === "claude"
-          ? settingsState?.claudeConfigDir ?? resolvedDirs.claude
-          : settingsState?.codexConfigDir ?? resolvedDirs.codex;
+          ? (settingsState?.claudeConfigDir ?? resolvedDirs.claude)
+          : (settingsState?.codexConfigDir ?? resolvedDirs.codex);
 
       try {
         const picked = await settingsApi.selectConfigDirectory(currentValue);
@@ -377,7 +387,8 @@ export function useSettings(): UseSettingsResult {
       ...data,
       showInTray: data.showInTray ?? true,
       minimizeToTrayOnClose: data.minimizeToTrayOnClose ?? true,
-      enableClaudePluginIntegration: data.enableClaudePluginIntegration ?? false,
+      enableClaudePluginIntegration:
+        data.enableClaudePluginIntegration ?? false,
       claudeConfigDir: sanitizeDir(data.claudeConfigDir),
       codexConfigDir: sanitizeDir(data.codexConfigDir),
       language: normalizedLanguage,
@@ -387,7 +398,8 @@ export function useSettings(): UseSettingsResult {
     syncLanguage(initialLanguageRef.current);
     setAppConfigDir(initialAppConfigDirRef.current);
     setResolvedDirs({
-      appConfig: initialAppConfigDirRef.current ?? defaultsRef.current.appConfig,
+      appConfig:
+        initialAppConfigDirRef.current ?? defaultsRef.current.appConfig,
       claude: normalized.claudeConfigDir ?? defaultsRef.current.claude,
       codex: normalized.codexConfigDir ?? defaultsRef.current.codex,
     });
@@ -423,7 +435,10 @@ export function useSettings(): UseSettingsResult {
           await settingsApi.applyClaudePluginConfig({ official: true });
         }
       } catch (error) {
-        console.warn("[useSettings] Failed to sync Claude plugin config", error);
+        console.warn(
+          "[useSettings] Failed to sync Claude plugin config",
+          error,
+        );
         toast.error(
           t("notifications.syncClaudePluginFailed", {
             defaultValue: "同步 Claude 插件失败",
@@ -436,7 +451,10 @@ export function useSettings(): UseSettingsResult {
           window.localStorage.setItem("language", payload.language as Language);
         }
       } catch (error) {
-        console.warn("[useSettings] Failed to persist language preference", error);
+        console.warn(
+          "[useSettings] Failed to persist language preference",
+          error,
+        );
       }
 
       initialLanguageRef.current = payload.language as Language;