feat(l1): APScheduler hourly cleanup job for abandoned L1 sessions

flip_stale_sessions flips L1WalkSession.status from 'active' to
'abandoned' for rows where last_step_at is older than 24h. Preserves the
row for audit; removes it from the L1 dashboard's 'Resume in progress'
widget. Runs hourly via APScheduler with max_instances=1 (Lesson 1).
Uses the admin session factory (no RLS context at startup).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/app/main.py

@@ -221,6 +221,18 @@ async def lifespan(app: FastAPI):
         max_instances=1,
     )
 
+    # L1 walk session cleanup: flip stale active sessions to 'abandoned' (hourly)
+    from app.services.l1_session_cleanup import run_cleanup_job as l1_cleanup_run
+    scheduler.add_job(
+        l1_cleanup_run,
+        trigger="interval",
+        hours=1,
+        id="l1_session_cleanup",
+        replace_existing=True,
+        max_instances=1,
+        args=[async_session_maker],
+    )
+
     # Auto-seed trees in background on PR environments
     seed_task = None
     if settings.SEED_ON_DEPLOY: