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/models/common/copilot.ts

@@ -46,6 +46,7 @@ export const ContextFileSchema = z.object({
   id: z.string(),
   chunkSize: z.number(),
   name: z.string(),
+  mimeType: z.string().optional(),
   status: ContextEmbedStatusSchema,
   error: z.string().nullable(),
   blobId: z.string(),
@@ -100,6 +101,9 @@ export type ChunkSimilarity = {
 
 export type FileChunkSimilarity = ChunkSimilarity & {
   fileId: string;
+  blobId: string;
+  name: string;
+  mimeType: string;
 };
 
 export type DocChunkSimilarity = ChunkSimilarity & {
@@ -108,6 +112,7 @@ export type DocChunkSimilarity = ChunkSimilarity & {
 
 export const CopilotWorkspaceFileSchema = z.object({
   fileName: z.string(),
+  blobId: z.string(),
   mimeType: z.string(),
   size: z.number(),
 });