Show full Grid-Review in Ground Truth step + GT badge in session list

- StepGroundTruth now shows the split view (original image + table)
  so the user can verify the final result before marking as GT
- Backend session list now returns is_ground_truth flag
- SessionList shows amber "GT" badge for marked sessions

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

klausur-service/backend/ocr_pipeline_session_store.py

@@ -262,14 +262,22 @@ async def list_sessions_db(
                    document_category, doc_type,
                    parent_session_id, box_index,
                    document_group_id, page_number,
-                   created_at, updated_at
+                   created_at, updated_at,
+                   ground_truth
             FROM ocr_pipeline_sessions
             {where}
             ORDER BY created_at DESC
             LIMIT $1
         """, limit)
 
-        return [_row_to_dict(row) for row in rows]
+        results = []
+        for row in rows:
+            d = _row_to_dict(row)
+            # Derive is_ground_truth flag from JSONB, then drop the heavy field
+            gt = d.pop("ground_truth", None) or {}
+            d["is_ground_truth"] = bool(gt.get("build_grid_reference"))
+            results.append(d)
+        return results
 
 
 async def get_sub_sessions(parent_session_id: str) -> List[Dict[str, Any]]: