docs(beat): backfill comments no longer claim errored jobs are retried

Follow-through on the tombstone rule (09e2772): the hourly/daily backfill
entries' comments still described the pre-fix retry-errored behavior.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CDgx8bQS5YrGRK76v8HUnM

backend/app/celery_app.py

@@ -115,13 +115,13 @@ def make_celery() -> Celery:
             },
             "enqueue-ccip-backfill-hourly": {
                 "task": "backend.app.tasks.ml.enqueue_gpu_backfill",
-                "schedule": 3600.0,  # auto-feed new images (+ retry errored) so
-                "args": ("ccip",),   # the queue keeps moving without the button
+                "schedule": 3600.0,  # auto-feed NEW images; errored are
+                "args": ("ccip",),   # tombstoned — retry is the button only
             },
             "enqueue-siglip-backfill-daily": {
                 "task": "backend.app.tasks.ml.enqueue_gpu_backfill",
-                "schedule": 86400.0,  # drain the concept-crop back-catalogue +
-                "args": ("siglip",),  # retry failed embeds, no button needed
+                "schedule": 86400.0,  # drain the concept-crop back-catalogue
+                "args": ("siglip",),  # (errored are tombstoned, not retried)
             },
             "enqueue-embed-backfill-daily": {
                 "task": "backend.app.tasks.ml.enqueue_gpu_backfill",