feat(server): improve context metadata & matching (#12064)

fix AI-20

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

- **New Features**
  - Enhanced file metadata with MIME type, blob ID, and file name across context and workspace, now visible in UI and API.
  - Added workspace-level matching for files and documents with configurable thresholds and workspace scoping in search queries.
  - Introduced a new error type and user-friendly messaging for global workspace context matching failures.

- **Bug Fixes**
  - Improved consistent handling of file MIME types and nullable context IDs for accurate metadata.

- **Documentation**
  - Updated GraphQL schema, queries, and mutations to include new metadata fields, optional parameters, and error types.

- **Style**
  - Added new localization strings for global context matching error messages.

- **Tests**
  - Extended test coverage with new and updated snapshot tests for metadata and matching logic.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/backend/server/src/plugins/copilot/context/service.ts

@@ -148,6 +148,48 @@ export class CopilotContextService implements OnApplicationBootstrap {
     return null;
   }
 
+  async matchWorkspaceFiles(
+    workspaceId: string,
+    content: string,
+    topK: number = 5,
+    signal?: AbortSignal,
+    threshold: number = 0.5
+  ) {
+    if (!this.embeddingClient) return [];
+    const embedding = await this.embeddingClient.getEmbedding(content, signal);
+    if (!embedding) return [];
+
+    const chunks = await this.models.copilotWorkspace.matchFileEmbedding(
+      workspaceId,
+      embedding,
+      topK * 2,
+      threshold
+    );
+
+    return this.embeddingClient.reRank(content, chunks, topK, signal);
+  }
+
+  async matchWorkspaceDocs(
+    workspaceId: string,
+    content: string,
+    topK: number = 5,
+    signal?: AbortSignal,
+    threshold: number = 0.5
+  ) {
+    if (!this.embeddingClient) return [];
+    const embedding = await this.embeddingClient.getEmbedding(content, signal);
+    if (!embedding) return [];
+
+    const workspace = await this.models.copilotContext.matchWorkspaceEmbedding(
+      embedding,
+      workspaceId,
+      topK * 2,
+      threshold
+    );
+
+    return this.embeddingClient.reRank(content, workspace, topK);
+  }
+
   @OnEvent('workspace.doc.embed.failed')
   async onDocEmbedFailed({
     contextId,