refactor(mcp): complete v3.7.0 cleanup - remove legacy code and warnings

This commit finalizes the v3.7.0 unified MCP architecture migration by
removing all deprecated code paths and eliminating compiler warnings.

Frontend Changes (~950 lines removed):
- Remove deprecated components: McpPanel, McpListItem, McpToggle
- Remove deprecated hook: useMcpActions
- Remove unused API methods: importFrom*, syncEnabledTo*, syncAllServers
- Simplify McpFormModal by removing dual-mode logic (unified/legacy)
- Remove syncOtherSide checkbox and conflict detection
- Clean up unused imports and state variables
- Delete associated test files

Backend Changes (~400 lines cleaned):
- Remove unused Tauri commands: import_mcp_from_*, sync_enabled_mcp_to_*
- Delete unused Gemini MCP functions: get_mcp_status, upsert/delete_mcp_server
- Add #[allow(deprecated)] to compatibility layer commands
- Add #[allow(dead_code)] to legacy helper functions for future migration
- Simplify boolean expression in mcp.rs per Clippy suggestion

API Deprecation:
- Mark legacy APIs with @deprecated JSDoc (getConfig, upsertServerInConfig, etc.)
- Preserve backward compatibility for v3.x, planned removal in v4.0

Verification:
- ✅ Zero TypeScript errors (pnpm typecheck)
- ✅ Zero Clippy warnings (cargo clippy)
- ✅ All code formatted (prettier + cargo fmt)
- ✅ Builds successfully

Total cleanup: ~1,350 lines of code removed/marked
Breaking changes: None (all legacy APIs still functional)

src/hooks/useMcp.ts

@@ -1,14 +1,14 @@
-import { useMutation, useQuery, useQueryClient } from '@tanstack/react-query';
-import { mcpApi } from '@/lib/api/mcp';
-import type { McpServer } from '@/types';
-import type { AppId } from '@/lib/api/types';
+import { useMutation, useQuery, useQueryClient } from "@tanstack/react-query";
+import { mcpApi } from "@/lib/api/mcp";
+import type { McpServer } from "@/types";
+import type { AppId } from "@/lib/api/types";
 
 /**
  * 查询所有 MCP 服务器（统一管理）
  */
 export function useAllMcpServers() {
   return useQuery({
-    queryKey: ['mcp', 'all'],
+    queryKey: ["mcp", "all"],
     queryFn: () => mcpApi.getAllServers(),
   });
 }
@@ -21,7 +21,7 @@ export function useUpsertMcpServer() {
   return useMutation({
     mutationFn: (server: McpServer) => mcpApi.upsertUnifiedServer(server),
     onSuccess: () => {
-      queryClient.invalidateQueries({ queryKey: ['mcp', 'all'] });
+      queryClient.invalidateQueries({ queryKey: ["mcp", "all"] });
     },
   });
 }
@@ -42,7 +42,7 @@ export function useToggleMcpApp() {
       enabled: boolean;
     }) => mcpApi.toggleApp(serverId, app, enabled),
     onSuccess: () => {
-      queryClient.invalidateQueries({ queryKey: ['mcp', 'all'] });
+      queryClient.invalidateQueries({ queryKey: ["mcp", "all"] });
     },
   });
 }
@@ -55,7 +55,7 @@ export function useDeleteMcpServer() {
   return useMutation({
     mutationFn: (id: string) => mcpApi.deleteUnifiedServer(id),
     onSuccess: () => {
-      queryClient.invalidateQueries({ queryKey: ['mcp', 'all'] });
+      queryClient.invalidateQueries({ queryKey: ["mcp", "all"] });
     },
   });
 }