feat(frontend): implement unified MCP panel for v3.7.0

Complete Phase 3 (P0) frontend implementation for unified MCP management:

**New Files:**
- src/hooks/useMcp.ts: React Query hooks for unified MCP operations
- src/components/mcp/UnifiedMcpPanel.tsx: Unified MCP management panel
- src/components/ui/checkbox.tsx: Checkbox component from shadcn/ui

**Features:**
- Unified panel with three-column layout: server info + app checkboxes + actions
- Multi-app control: Claude/Codex/Gemini checkboxes for each server
- Real-time stats: Show enabled server counts per app
- Full CRUD operations: Add, edit, delete, sync all servers

**Integration:**
- Replace old app-specific McpPanel with UnifiedMcpPanel in App.tsx
- Update McpFormModal to support unified mode with apps field
- Add i18n support: mcp.unifiedPanel namespace (zh/en)

**Type Safety:**
- Ensure McpServer.apps field always initialized
- Fix all test files to include apps field
- TypeScript type check passes ✅

**Architecture:**
- Single source of truth: mcp.servers manages all MCP configs
- Per-server app control: apps.claude/codex/gemini boolean flags
- Backward compatible: McpFormModal supports both unified and legacy modes

Next: P1 tasks (import dialogs, sub-components, tests)

src/hooks/useMcp.ts

@@ -0,0 +1,70 @@
+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'],
+    queryFn: () => mcpApi.getAllServers(),
+  });
+}
+
+/**
+ * 添加或更新 MCP 服务器
+ */
+export function useUpsertMcpServer() {
+  const queryClient = useQueryClient();
+  return useMutation({
+    mutationFn: (server: McpServer) => mcpApi.upsertUnifiedServer(server),
+    onSuccess: () => {
+      queryClient.invalidateQueries({ queryKey: ['mcp', 'all'] });
+    },
+  });
+}
+
+/**
+ * 切换 MCP 服务器在特定应用的启用状态
+ */
+export function useToggleMcpApp() {
+  const queryClient = useQueryClient();
+  return useMutation({
+    mutationFn: ({
+      serverId,
+      app,
+      enabled,
+    }: {
+      serverId: string;
+      app: AppId;
+      enabled: boolean;
+    }) => mcpApi.toggleApp(serverId, app, enabled),
+    onSuccess: () => {
+      queryClient.invalidateQueries({ queryKey: ['mcp', 'all'] });
+    },
+  });
+}
+
+/**
+ * 删除 MCP 服务器
+ */
+export function useDeleteMcpServer() {
+  const queryClient = useQueryClient();
+  return useMutation({
+    mutationFn: (id: string) => mcpApi.deleteUnifiedServer(id),
+    onSuccess: () => {
+      queryClient.invalidateQueries({ queryKey: ['mcp', 'all'] });
+    },
+  });
+}
+
+/**
+ * 同步所有启用的 MCP 服务器到各应用的 live 配置
+ */
+export function useSyncAllMcpServers() {
+  return useMutation({
+    mutationFn: () => mcpApi.syncAllServers(),
+  });
+}