feat(ccip): read-only observability API for the crop/CCIP work (#114)

So the work can be checked through an API as the agent fills in vectors (same
pattern as /api/heads/metrics):
- GET /api/ccip/overview: regions by kind, images with figure CCIP vectors, the
  per-character reference counts (which characters have enough examples to match
  on), and the embedding versions present.
- GET /api/ccip/images/<id>: that image's stored regions (bbox, frame_time,
  has_ccip/has_siglip, versions) + the CCIP character matches it would get — for
  spot-checking detector + matcher output.

Read-only, no GPU. (Queue depth is already at /api/gpu/status.)

Tests: overview coverage counts + per-character refs; per-image regions + matches.

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

backend/app/api/__init__.py

@@ -24,6 +24,7 @@ def all_blueprints() -> list[Blueprint]:
     from .credentials import credentials_bp
     from .downloads import downloads_bp
     from .extension import extension_bp
+    from .ccip import ccip_bp
     from .gallery import gallery_bp
     from .gpu import gpu_bp
     from .heads import heads_bp
@@ -62,6 +63,7 @@ def all_blueprints() -> list[Blueprint]:
         tag_eval_bp,
         heads_bp,
         gpu_bp,
+        ccip_bp,
         ml_admin_bp,
         thumbnails_bp,
         sources_bp,