feat(mcp): add import button to import MCP servers from apps

- Add import_mcp_from_apps command that reuses existing import logic
- Add Import button in MCP panel header (consistent with Skills)
- Fix import count to only return truly new servers (not already in DB)
- Update translations for import success/no-import messages (zh/en/ja)

src/lib/api/mcp.ts

@@ -119,4 +119,11 @@ export const mcpApi = {
   ): Promise<void> {
     return await invoke("toggle_mcp_app", { serverId, app, enabled });
   },
+
+  /**
+   * 从所有应用导入 MCP 服务器
+   */
+  async importFromApps(): Promise<number> {
+    return await invoke("import_mcp_from_apps");
+  },
 };