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- Clean up `src/vite-env.d.ts` (remove 156 lines of outdated types)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/components/settings/AboutSection.tsx

@@ -59,8 +59,8 @@ export function AboutSection({ isPortable }: AboutSectionProps) {
       const displayVersion = targetVersion.startsWith("v")
         ? targetVersion
         : targetVersion
-        ? `v${targetVersion}`
-        : "";
+          ? `v${targetVersion}`
+          : "";
 
       if (!displayVersion) {
         await settingsApi.openExternal(
@@ -108,7 +108,10 @@ export function AboutSection({ isPortable }: AboutSectionProps) {
         try {
           await settingsApi.checkUpdates();
         } catch (fallbackError) {
-          console.error("[AboutSection] Failed to open fallback updater", fallbackError);
+          console.error(
+            "[AboutSection] Failed to open fallback updater",
+            fallbackError,
+          );
         }
       } finally {
         setIsDownloading(false);
@@ -119,9 +122,7 @@ export function AboutSection({ isPortable }: AboutSectionProps) {
     try {
       const available = await checkUpdate();
       if (!available) {
-        toast.success(
-          t("settings.upToDate", { defaultValue: "已是最新版本" }),
-        );
+        toast.success(t("settings.upToDate", { defaultValue: "已是最新版本" }));
       }
     } catch (error) {
       console.error("[AboutSection] Check update failed", error);
@@ -131,14 +132,7 @@ export function AboutSection({ isPortable }: AboutSectionProps) {
         }),
       );
     }
-  }, [
-    checkUpdate,
-    hasUpdate,
-    isPortable,
-    resetDismiss,
-    t,
-    updateHandle,
-  ]);
+  }, [checkUpdate, hasUpdate, isPortable, resetDismiss, t, updateHandle]);
 
   const displayVersion =
     version ?? t("common.unknown", { defaultValue: "未知" });