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- Clean up `src/vite-env.d.ts` (remove 156 lines of outdated types)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

@@ -1,10 +1,9 @@
 import React, { useCallback, useEffect, useMemo, useState } from "react";
 import { useTranslation } from "react-i18next";
 import { Zap, Loader2, Plus, X, AlertCircle, Save } from "lucide-react";
+import { vscodeApi, type AppType } from "@/lib/api";
 import { isLinux } from "../../lib/platform";
 
-import type { AppType } from "../../lib/tauri-api";
-
 export interface EndpointCandidate {
   id?: string;
   url: string;
@@ -94,7 +93,7 @@ const EndpointSpeedTest: React.FC<EndpointSpeedTestProps> = ({
     const loadCustomEndpoints = async () => {
       try {
         if (!providerId) return;
-        const customEndpoints = await window.api.getCustomEndpoints(
+        const customEndpoints = await vscodeApi.getCustomEndpoints(
           appType,
           providerId,
         );
@@ -251,7 +250,7 @@ const EndpointSpeedTest: React.FC<EndpointSpeedTestProps> = ({
     // 保存到后端
     try {
       if (providerId) {
-        await window.api.addCustomEndpoint(appType, providerId, sanitized);
+        await vscodeApi.addCustomEndpoint(appType, providerId, sanitized);
       }
 
       // 更新本地状态
@@ -295,7 +294,7 @@ const EndpointSpeedTest: React.FC<EndpointSpeedTestProps> = ({
       // 如果是自定义端点，尝试从后端删除（无 providerId 则仅本地删除）
       if (entry.isCustom && providerId) {
         try {
-          await window.api.removeCustomEndpoint(appType, providerId, entry.url);
+          await vscodeApi.removeCustomEndpoint(appType, providerId, entry.url);
         } catch (error) {
           console.error(t("endpointTest.removeEndpointFailed"), error);
           return;
@@ -322,7 +321,7 @@ const EndpointSpeedTest: React.FC<EndpointSpeedTestProps> = ({
       return;
     }
 
-    if (typeof window === "undefined" || !window.api?.testApiEndpoints) {
+    if (typeof window === "undefined") {
       setLastError(t("endpointTest.testUnavailable"));
       return;
     }
@@ -341,7 +340,7 @@ const EndpointSpeedTest: React.FC<EndpointSpeedTestProps> = ({
     );
 
     try {
-      const results = await window.api.testApiEndpoints(urls, {
+      const results = await vscodeApi.testApiEndpoints(urls, {
         timeoutSecs: appType === "codex" ? 12 : 8,
       });
       const resultMap = new Map(
@@ -400,7 +399,7 @@ const EndpointSpeedTest: React.FC<EndpointSpeedTestProps> = ({
       // 更新最后使用时间（对自定义端点）
       const entry = entries.find((e) => e.url === url);
       if (entry?.isCustom && providerId) {
-        await window.api.updateEndpointLastUsed(appType, providerId, url);
+        await vscodeApi.updateEndpointLastUsed(appType, providerId, url);
       }
 
       onChange(url);