fix: set account_id on all Session constructors; fix 3 ESLint errors in CI

Backend: start_session, prepare_session, batch_launch_sessions all missing
account_id=current_user.account_id — Phase 1 NOT NULL constraint made these
500 in test suite (test_ratings.py fixture couldn't create sessions).

Frontend ESLint:
- TaskLane.tsx: suppress react-refresh/only-export-components for clearTaskState
- TeamSummary.tsx: init loading from isAccountOwner to avoid sync setState in effect
- ScriptBodyEditor.tsx: move lastValueRef.current assignment into useEffect

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/components/assistant/TaskLane.tsx

@@ -57,6 +57,7 @@ function loadTaskState(sessionId: string): TaskResponse[] | null {
   } catch { return null }
 }
 
+// eslint-disable-next-line react-refresh/only-export-components
 export function clearTaskState(sessionId: string) {
   try { sessionStorage.removeItem(`${TASK_LANE_STORAGE_KEY}:${sessionId}`) } catch { /* ignore */ }
 }