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/models/ml_settings.py

@@ -92,6 +92,15 @@ class MLSettings(Base):
     ccip_match_threshold: Mapped[float] = mapped_column(
         Float, nullable=False, default=0.85
     )
+    # CCIP auto-apply (#114). Confident matches (>= ccip_auto_apply_threshold,
+    # above the suggest cut) auto-tag on a daily sweep. ON by default (opt-out);
+    # single-character references + the high bar keep it safe, every tag reversible.
+    ccip_auto_apply_enabled: Mapped[bool] = mapped_column(
+        Boolean, nullable=False, default=True
+    )
+    ccip_auto_apply_threshold: Mapped[float] = mapped_column(
+        Float, nullable=False, default=0.92
+    )
     tagger_model_version: Mapped[str] = mapped_column(
         String(128), nullable=False, default="camie-tagger-v2"
     )