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- Clean up `src/vite-env.d.ts` (remove 156 lines of outdated types)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

@@ -1,7 +1,13 @@
 import { useCallback, useEffect, useMemo, useState } from "react";
 import { Loader2, Save } from "lucide-react";
 import { toast } from "sonner";
-import { Dialog, DialogContent, DialogFooter, DialogHeader, DialogTitle } from "@/components/ui/dialog";
+import {
+  Dialog,
+  DialogContent,
+  DialogFooter,
+  DialogHeader,
+  DialogTitle,
+} from "@/components/ui/dialog";
 import { Tabs, TabsContent, TabsList, TabsTrigger } from "@/components/ui/tabs";
 import { Button } from "@/components/ui/button";
 import { settingsApi } from "@/lib/api";
@@ -84,7 +90,13 @@ export function SettingsDialog({
     clearSelection();
     resetStatus();
     onOpenChange(false);
-  }, [acknowledgeRestart, clearSelection, onOpenChange, resetSettings, resetStatus]);
+  }, [
+    acknowledgeRestart,
+    clearSelection,
+    onOpenChange,
+    resetSettings,
+    resetStatus,
+  ]);
 
   const handleDialogChange = useCallback(
     (nextOpen: boolean) => {
@@ -173,9 +185,7 @@ export function SettingsDialog({
                 <TabsTrigger value="advanced">
                   {t("settings.tabAdvanced", { defaultValue: "高级" })}
                 </TabsTrigger>
-                <TabsTrigger value="about">
-                  {t("common.about")}
-                </TabsTrigger>
+                <TabsTrigger value="about">{t("common.about")}</TabsTrigger>
               </TabsList>
 
               <div className="flex-1 overflow-y-auto pr-1">