feat(gateway): Add cron job provisioning

Create a mission control runner cron job via the gateway HTTP API\nand ensure it is present on startup. Adds cron helpers, job\nbuilder, and a startup hook.\n\nCo-Authored-By: Claude <noreply@anthropic.com>

backend/app/main.py

@@ -12,6 +12,7 @@ from app.api.tasks import router as tasks_router
 from app.core.config import settings
 from app.core.logging import configure_logging
 from app.db.session import init_db
+from app.services.cron_jobs import ensure_mission_control_cron_job
 
 configure_logging()
 
@@ -29,8 +30,9 @@ if origins:
 
 
 @app.on_event("startup")
-def on_startup() -> None:
+async def on_startup() -> None:
     init_db()
+    await ensure_mission_control_cron_job()
 
 
 @app.get("/health")