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>

backend/app/api/endpoints/sessions.py

@@ -196,6 +196,7 @@ async def start_session(
     new_session = Session(
         tree_id=tree.id,
         user_id=current_user.id,
+        account_id=current_user.account_id,
         tree_snapshot=tree_snapshot,
         path_taken=[],
         decisions=[],
@@ -693,6 +694,7 @@ async def prepare_session(
     new_session = Session(
         tree_id=tree.id,
         user_id=data.assigned_to_id or current_user.id,
+        account_id=current_user.account_id,
         tree_snapshot=tree_snapshot,
         path_taken=[],
         decisions=[],
@@ -770,6 +772,7 @@ async def batch_launch_sessions(
         session = Session(
             tree_id=tree.id,
             user_id=current_user.id,
+            account_id=current_user.account_id,
             tree_snapshot=tree_snapshot,
             path_taken=[],
             decisions=[],