feat(mcp): integrate MCP Server into backend service as built-in endpoint

- Add MCP Controller and register /mcp route
- MCP Server now uses OpenAPI Token for authentication
- Update frontend settings to show built-in MCP endpoint config
- Update docs to reflect integrated MCP endpoint

internal/router/register.go

@@ -72,6 +72,7 @@ func RegisterControllers() *Controllers {
 		Interconnect: controllers.NewInterconnectController(interconnectService),
 		Data:         controllers.NewDataController(taskController, envController),
 		Install:      controllers.NewInstallController(),
+		MCP:          controllers.NewMCPController(),
 	}
 }