fix(server): frequent embedding (#13475)

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

- New Features
- Smarter embedding pipeline skips re-embedding when content hasn’t
changed; added content sanitization for embeddings and workspace content
retrieval.
- Bug Fixes
- Re-embedding now requires both a document update and the last
embedding being older than 10 minutes, reducing unnecessary work.
- Refactor
- Consolidated embedding preprocessing and moved sanitization utilities
into shared models; upserts now refresh stored content.
- Tests
- Expanded snapshot-based tests covering multiple time/age scenarios for
embedding decision logic.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/backend/server/src/plugins/copilot/mcp/provider.ts

@@ -6,9 +6,9 @@ import z from 'zod';
 
 import { DocReader } from '../../../core/doc';
 import { AccessController } from '../../../core/permission';
+import { clearEmbeddingChunk } from '../../../models';
 import { IndexerService } from '../../indexer';
 import { CopilotContextService } from '../context';
-import { clearEmbeddingChunk } from '../utils';
 
 @Injectable()
 export class WorkspaceMcpProvider {