move job scheduling to DB

backend/app/tasks/celery_app.py

@@ -28,10 +28,13 @@ celery_app.conf.update(
 )
 
 # Celery Beat schedule for periodic tasks
+# Note: The scheduler runs frequently (every 60s) but only triggers downloads
+# for sources whose individual check_interval has elapsed. Per-source intervals
+# are stored in the database and can be configured via the UI.
 celery_app.conf.beat_schedule = {
-    "check-sources-hourly": {
+    "check-sources-scheduler": {
         "task": "app.tasks.downloads.scheduled_check",
-        "schedule": settings.default_check_interval,  # Default: every hour
+        "schedule": 60,  # Run every 60 seconds to check for due sources
     },
     "cleanup-old-downloads-daily": {
         "task": "app.tasks.downloads.cleanup_old_downloads",