refactor: clean up imports and improve session key assertion formatting

backend/app/services/board_lifecycle.py

@@ -109,4 +109,3 @@ async def delete_board(session: AsyncSession, *, board: Board) -> OkResponse:
     await session.delete(board)
     await session.commit()
     return OkResponse()
-

backend/app/services/openclaw/gateway_dispatch.py

@@ -12,8 +12,8 @@ from app.models.boards import Board
 from app.models.gateways import Gateway
 from app.services.openclaw.db_service import OpenClawDBService
 from app.services.openclaw.gateway_resolver import (
-    get_gateway_for_board,
     gateway_client_config,
+    get_gateway_for_board,
     optional_gateway_client_config,
     require_gateway_for_board,
 )