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/workspace/service.ts

@@ -60,6 +60,7 @@ export class CopilotWorkspaceService implements OnApplicationBootstrap {
     await this.storage.put(userId, workspaceId, blobId, buffer);
     const file = await this.models.copilotWorkspace.addFile(workspaceId, {
       fileName,
+      blobId,
       mimeType: content.mimetype,
       size: buffer.length,
     });

packages/backend/server/src/plugins/copilot/workspace/types.ts

@@ -55,6 +55,9 @@ export class CopilotWorkspaceFileType implements CopilotWorkspaceFile {
   @Field(() => String)
   fileId!: string;
 
+  @Field(() => String)
+  blobId!: string;
+
   @Field(() => String)
   fileName!: string;