feat: add CronJob and CronJobRun models with bulk upsert API and admin

- CronJob: maps jobs.json (schedule, payload, delivery, state fields)
- CronJobRun: stores runs/*.jsonl per-job execution history with usage/tokens
- cron_bulk_upsert service: atomic upsert with GET_OR_CREATE for idempotency
- POST /api/cron/bulk_upsert/ endpoint
- Django Admin: CronJobAdmin with CronJobRunInline, CronJobRunAdmin
- sync_sessions.py --cron mode: SSH read jobs.json + runs/*.jsonl, incremental sync
- 0003_cronjob_cronjobrun migration

src/openclaw/urls.py

@@ -1,6 +1,8 @@
 from django.urls import path
 from openclaw.views import sessions_bulk_upsert
+from openclaw.cron_views import cron_bulk_upsert
 
 urlpatterns = [
     path("sessions/bulk_upsert/", sessions_bulk_upsert, name="sessions_bulk_upsert"),
+    path("cron/bulk_upsert/", cron_bulk_upsert, name="cron_bulk_upsert"),
 ]