feat(agent): crop proposers — booru_yolo anatomy + COCO person + comic panels (#1202)

Better region PROPOSERS feeding the existing crop→SigLIP→max-over-bag heads (no
change to the learned-tagging approach; no per-tag cost — propose once, embed
each region, all heads in one matmul).

- detectors.py: lazy ultralytics YOLO wrapper, each proposer independently
  optional + guarded (a bad weight spec / inference error self-disables that one,
  logged, never breaks the worker). Weights resolve from an ultralytics name |
  http(s) URL | "hf_repo::file", cached under HF_HOME. NMS merge so a figure two
  detectors both find collapses to one crop.
- worker: figure boxes = imgutils detect_person ∪ general COCO person (merged)
  → CCIP + concept (anime + Western/realistic coverage); booru_yolo anatomy
  components (head/cat-head/anatomy/…) → concept crops; comic panels → kind=
  'panel' concept crops. Capped per frame (MAX_COMPONENTS/MAX_PANELS).
- config + compose: PERSON_WEIGHTS (default yolo11n.pt, works OOB),
  ANATOMY_WEIGHTS + PANEL_WEIGHTS (operator sets booru_yolo URL + mosesb panel
  hf::file; empty = off). ultralytics added to requirements.
- backend: image_region 'kind' doc notes 'panel'; no migration (free String,
  and the bag scorer keys on a non-null siglip_embedding, not the kind, so any
  SigLIP region joins the bag automatically).

Agent is outside CI — py-compiled here; operator tests on the GPU and checks
Western-vs-anime crop quality via /api/ccip observability.

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

backend/app/models/image_region.py

@@ -31,7 +31,10 @@ class ImageRegion(Base):
         ForeignKey("image_record.id", ondelete="CASCADE"), index=True
     )
     # 'frame' (a whole video frame → SigLIP bag) | 'face' | 'figure' (→ CCIP
-    # character id) | 'concept' (→ SigLIP head bag).
+    # character id) | 'concept' (→ SigLIP head bag) | 'panel' (a comic panel crop,
+    # also SigLIP → the bag). Free String, not an enum — proposers can add kinds
+    # without a migration; the bag scorer keys on a non-null siglip_embedding, not
+    # the kind, so any SigLIP-embedded region joins the bag.
     kind: Mapped[str] = mapped_column(String(16), nullable=False)
     # For video/animated media: the source frame's timestamp in SECONDS. NULL for
     # static images. Lets a video be a BAG of per-frame instances (fixes the