feat(server): basic mcp server (#13298)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Introduced a new endpoint for MCP (Model Context Protocol) server
interaction under `/api/workspaces/:workspaceId/mcp`, enabling advanced
document reading and search capabilities within workspaces.
* Added support for semantic and keyword search tools, as well as
document reading through the MCP server, with user access control and
input validation.

* **Improvements**
* Enhanced metadata handling in semantic search results for improved
clarity.
* Streamlined internal imports and refactored utility functions for
better maintainability.

* **Chores**
  * Added a new SDK dependency to the backend server package.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/backend/server/src/plugins/copilot/index.ts

@@ -17,6 +17,8 @@ import {
 import { CopilotController } from './controller';
 import { CopilotCronJobs } from './cron';
 import { CopilotEmbeddingJob } from './embedding';
+import { WorkspaceMcpController } from './mcp/controller';
+import { WorkspaceMcpProvider } from './mcp/provider';
 import { ChatMessageCache } from './message';
 import { PromptService } from './prompt';
 import { CopilotProviderFactory, CopilotProviders } from './providers';
@@ -78,7 +80,9 @@ import {
     UserCopilotResolver,
     PromptsManagementResolver,
     CopilotContextRootResolver,
+    // mcp
+    WorkspaceMcpProvider,
   ],
-  controllers: [CopilotController],
+  controllers: [CopilotController, WorkspaceMcpController],
 })
 export class CopilotModule {}