feat(regions): image_region storage + service for the crop pipeline (#114 slice 2)

The storage backbone both crop jobs write to and read from. image_region =
normalized bbox (rx/ry/rw/rh) + kind ('face'/'figure' → CCIP character id;
'concept' → SigLIP head bag) + the crop's embedding (nullable Vector(768) CCIP /
Vector(1152) SigLIP, one per kind) + version stamps for compute-once gating. The
bbox doubles as grounded-tag provenance. Migration 0061.

RegionService.replace_regions (scoped BY KIND so the figure + concept pipelines
don't clobber each other) + get_regions — the GPU agent's results endpoint will
call the writer; the character matcher + bag scorer read. Server-side, no GPU.

Tests: replace/get round-trip, kind-scoped replacement, CCIP vector round-trip.

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

backend/app/services/ml/regions.py

@@ -0,0 +1,58 @@
+"""Region read/write for the crop pipeline (#114).
+
+The GPU agent's results endpoint calls replace_regions() to store a freshly
+detected/embedded set; the character matcher + concept-bag scorer read via
+get_regions(). Replacement is scoped BY KIND so the figure pipeline and the
+concept pipeline don't clobber each other.
+"""
+
+from typing import Any
+
+from sqlalchemy import delete, select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from ...models import ImageRegion
+
+
+class RegionService:
+    def __init__(self, session: AsyncSession):
+        self.session = session
+
+    async def get_regions(
+        self, image_id: int, kinds: list[str] | None = None
+    ) -> list[ImageRegion]:
+        stmt = select(ImageRegion).where(ImageRegion.image_record_id == image_id)
+        if kinds:
+            stmt = stmt.where(ImageRegion.kind.in_(kinds))
+        return list(
+            (await self.session.execute(stmt.order_by(ImageRegion.id))).scalars()
+        )
+
+    async def replace_regions(
+        self, image_id: int, kinds: list[str], regions: list[dict[str, Any]]
+    ) -> int:
+        """Replace this image's regions OF THE GIVEN KINDS with `regions` (a
+        re-detect/re-propose supersedes the prior set without touching other
+        kinds). Each region dict: {kind, bbox:(x,y,w,h), score?, detector_version?,
+        crop_version?, embedding_version?, ccip_embedding?, siglip_embedding?}.
+        Returns the number inserted."""
+        await self.session.execute(
+            delete(ImageRegion)
+            .where(ImageRegion.image_record_id == image_id)
+            .where(ImageRegion.kind.in_(kinds))
+        )
+        n = 0
+        for r in regions:
+            rx, ry, rw, rh = r["bbox"]
+            self.session.add(ImageRegion(
+                image_record_id=image_id, kind=r["kind"],
+                rx=rx, ry=ry, rw=rw, rh=rh,
+                score=r.get("score"),
+                detector_version=r.get("detector_version"),
+                crop_version=r.get("crop_version"),
+                embedding_version=r.get("embedding_version"),
+                ccip_embedding=r.get("ccip_embedding"),
+                siglip_embedding=r.get("siglip_embedding"),
+            ))
+            n += 1
+        return n