perf(api,frontend): index hot queries, paginate chats, fix realtime

backend/src/utils/policy/repository.py

@@ -85,6 +85,18 @@ async def list_folders(pool: asyncpg.Pool, account_id: int) -> list[FolderSpec]:
     return [_row_to_folder(row) for row in rows]
 
 
+async def get_folder(
+    pool: asyncpg.Pool, account_id: int, folder_id: int
+) -> FolderSpec | None:
+    row = await pool.fetchrow(
+        "SELECT folder_id, title, order_index, is_chatlist, raw "
+        "FROM folders WHERE account_id = $1 AND folder_id = $2",
+        account_id,
+        folder_id,
+    )
+    return _row_to_folder(row) if row else None
+
+
 async def create_policy(
     pool: asyncpg.Pool,
     account_id: int | None,