feat(ml): schedule presentation auto-hide sweep + retention (#141 step 6)

scheduled_presentation_auto_apply (daily beat) runs presentation_auto_apply_sweep
— idempotent, so an interrupted run just re-runs next cycle (that's the recovery),
wall-clock bounded by soft/hard task time limits. prune_presentation_reviews
(daily beat) drops RESOLVED review flags older than 30 days (rule 89 retention).
Tests run both tasks via a monkeypatched session factory. Milestone 141 complete:
the presentation-chrome auto-hide + conflict-flagged review is now live end-to-end.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CDgx8bQS5YrGRK76v8HUnM

backend/app/celery_app.py

@@ -152,6 +152,15 @@ def make_celery() -> Celery:
                 "schedule": 86400.0,  # soft auto-apply: drop auto-tags now below
                 # their threshold (m139); no-op unless the auto-apply switch is on
             },
+            "presentation-auto-apply-daily": {
+                "task": "backend.app.tasks.ml.scheduled_presentation_auto_apply",
+                "schedule": 86400.0,  # auto-hide banner/editor chrome (#141);
+                # no-op unless presentation_auto_apply_enabled
+            },
+            "prune-presentation-reviews-daily": {
+                "task": "backend.app.tasks.ml.prune_presentation_reviews",
+                "schedule": 86400.0,  # retention: drop resolved review flags >30d
+            },
             "snapshot-head-metrics-daily": {
                 "task": "backend.app.tasks.maintenance.snapshot_head_metrics",
                 "schedule": 86400.0,