feat(ccip): automation + reference quality — keep identity flowing hands-free (#114)

Works through the optional CCIP ideas + the "keep moving even if I forget" ask:

AUTOMATION (no button needed):
- Hourly beat auto-enqueues CCIP backfill — new images get embedded (and errored
  ones retried) on their own; the queue never goes idle waiting for a click.
- CCIP auto-apply: a daily sweep tags confident matches (source='ccip_auto') so
  identity tags keep flowing. ON by default (opt-out, like head auto-apply);
  ml_settings.ccip_auto_apply_enabled + _threshold (0.92, above the suggest cut),
  migration 0064. Vectorized (one matmul + reduceat per image), reversible, skips
  already-applied/rejected. Switch + threshold in the GPU agent card; GET/PATCH
  /api/ml/settings; auto_applied count in /api/ccip/overview.

REFERENCE QUALITY (the over-fire root cause):
- character_references now draws ONLY from single-character images — on a
  multi-character image the tag is image-level, so every figure would otherwise
  pollute each character's prototypes (a 2-char image tagged 'Velma' made
  Daphne's figure a Velma reference). This is the contamination behind residual
  over-firing.
- Cached on a cheap signature (char-tag count + ccip-region count/max-id) so the
  reference load isn't redone on every modal open.

Tests: multi-character image not used as a reference; auto-apply tags a confident
match as ccip_auto.

NEXT (not done, confirmed): comic-panel cropping + SigLIP concept crops ("spot
interesting content").

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ttrj5P7upUTueSfoJcxEqa

backend/app/celery_app.py

@@ -121,6 +121,15 @@ def make_celery() -> Celery:
                 "task": "backend.app.tasks.ml.recover_orphaned_gpu_jobs",
                 "schedule": 60.0,  # quick pickup of work a dead agent orphaned
             },
+            "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
+            },
+            "ccip-auto-apply-daily": {
+                "task": "backend.app.tasks.ml.scheduled_ccip_auto_apply",
+                "schedule": 86400.0,  # no-op unless ccip_auto_apply_enabled
+            },
             "snapshot-head-metrics-daily": {
                 "task": "backend.app.tasks.maintenance.snapshot_head_metrics",
                 "schedule": 86400.0,