refactor(mcp): redesign MCP management panel UI

- Redesign MCP panel to match main interface style
- Add toggle switch for each MCP server to enable/disable
- Use emerald theme color consistent with MCP button
- Create card-based layout with one MCP per row
- Add dedicated form modal for add/edit operations
- Implement proper empty state with friendly prompts
- Add comprehensive i18n support (zh/en)
- Extend McpServer type to support enabled field
- Backend already supports enabled field via serde_json::Value

Components:
- McpPanel: Main panel container with header and list
- McpListItem: Card-based list item with toggle and actions
- McpFormModal: Independent modal for add/edit forms
- McpToggle: Emerald-themed toggle switch component

All changes passed TypeScript type checking and production build.

src/lib/tauri-api.ts

@@ -1,6 +1,12 @@
 import { invoke } from "@tauri-apps/api/core";
 import { listen, UnlistenFn } from "@tauri-apps/api/event";
-import { Provider, Settings, CustomEndpoint, McpStatus, McpServer } from "../types";
+import {
+  Provider,
+  Settings,
+  CustomEndpoint,
+  McpStatus,
+  McpServer,
+} from "../types";
 
 // 应用类型
 export type AppType = "claude" | "codex";