feat(backend): add single-record draft read endpoints

add backend read endpoints for single draft records

support direct fetch of individual draft entities
improve draft inspection and targeted editor workflows

backend/app/repositories/scheme_groups.py

@@ -166,3 +166,26 @@ async def delete_scheme_version_group_by_record_id(
 
         await session.delete(group)
         await session.commit()
+
+
+async def get_scheme_version_group_by_record_id(
+    *,
+    scheme_version_id: str,
+    group_record_id: str,
+) -> SchemeGroupRecord:
+    async with AsyncSessionLocal() as session:
+        result = await session.execute(
+            select(SchemeGroupRecord).where(
+                SchemeGroupRecord.scheme_version_id == scheme_version_id,
+                SchemeGroupRecord.group_record_id == group_record_id,
+            )
+        )
+        row = result.scalar_one_or_none()
+
+        if row is None:
+            raise HTTPException(
+                status_code=status.HTTP_404_NOT_FOUND,
+                detail="Group record not found in current draft version",
+            )
+
+        return row