feat(core): peek doc in ai doc-read tool result (#13424)

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

## Summary by CodeRabbit

* **New Features**
* Enhanced document read results with clickable cards that open a peek
view of the referenced document.
* Added support for displaying document identifiers in document read
results.

* **Bug Fixes**
* Improved compatibility with older document read results that may lack
a document identifier.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/backend/server/src/plugins/copilot/tools/doc-read.ts

@@ -57,6 +57,7 @@ export const buildDocContentGetter = (
     }
 
     return {
+      docId,
       title: content.title,
       markdown: content.markdown,
       createdAt: docMeta.createdAt,