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/base/error/def.ts

@@ -714,6 +714,12 @@ export const USER_FRIENDLY_ERRORS = {
     message: ({ contextId, content, message }) =>
       `Failed to match context ${contextId} with "${escape(content)}": ${message}`,
   },
+  copilot_failed_to_match_global_context: {
+    type: 'internal_server_error',
+    args: { workspaceId: 'string', content: 'string', message: 'string' },
+    message: ({ workspaceId, content, message }) =>
+      `Failed to match context in workspace ${workspaceId} with "${escape(content)}": ${message}`,
+  },
   copilot_embedding_disabled: {
     type: 'action_forbidden',
     message: `Embedding feature is disabled, please contact the administrator to enable it in the workspace settings.`,