Fix _sync xattr field name: use _deleted instead of deleted

The Sync Gateway _sync xattr uses `_deleted` (with underscore) not
`deleted` as the field name to indicate tombstone status.

Changes:
- Query `_sync._deleted` instead of `_sync.deleted`
- Add WARNING comment that querying _sync directly is unsupported in production
- Reference Sync Gateway documentation on shared bucket access

This fix enables proper detection of tombstones vs live documents
in CBS when using shared bucket access mode.

According to Sync Gateway docs, the _sync structure is internal and
can change between versions. Direct N1QL queries on _sync should only
be used for testing/debugging, not in production applications.

References:
- https://docs.couchbase.com/sync-gateway/current/shared-bucket-access.html
- Sync Gateway GitHub issues discussing _sync structure

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: pimpin

examples/utils/cbs_admin.rs

@@ -44,9 +44,13 @@ pub fn check_doc_in_cbs(doc_id: &str) {
     // Use port 8093 for Query service (not 8091 which is admin/REST API)
     // Query XATTRs to see tombstones in shared bucket access mode
     // The _sync xattr contains Sync Gateway metadata including deleted status
+    //
+    // WARNING: Querying _sync xattr directly is UNSUPPORTED in production per Sync Gateway docs
+    // This is only for testing/debugging purposes. The _sync structure can change between versions.
+    // Reference: https://docs.couchbase.com/sync-gateway/current/shared-bucket-access.html
     let url = "http://localhost:8093/query/service";
     let query = format!(
-        "SELECT META().id, META().xattrs._sync.deleted as deleted FROM `{CBS_BUCKET}` USE KEYS ['{doc_id}']"
+        "SELECT META().id, META().xattrs._sync._deleted as deleted FROM `{CBS_BUCKET}` USE KEYS ['{doc_id}']"
     );
     let body = serde_json::json!({"statement": query});