feat(vision): immagini di riferimento non orfane, GET/DELETE (#38.5)

save_reference_image scrive il file dopo il flush riuscito; il router
lo cancella se il commit successivo fallisce. Aggiunti GET
/api/vision/reference-images?task_id= (lista, Maker) e DELETE
/api/vision/reference-images/{id} (cancella riga e file, Maker).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/backend/models/api/vision.py

@@ -1,5 +1,7 @@
 """Pydantic schemas for the vision execution response."""
-from pydantic import BaseModel
+from datetime import datetime
+
+from pydantic import BaseModel, ConfigDict
 
 
 class VisionMeasurementResult(BaseModel):
@@ -14,3 +16,16 @@ class VisionExecuteResponse(BaseModel):
     vision_result_id: int
     engine_version: str
     measurements: list[VisionMeasurementResult]
+
+
+class VisionReferenceImageResponse(BaseModel):
+    """One saved reference image, as `GET /api/vision/reference-images` lists it."""
+    model_config = ConfigDict(from_attributes=True)
+
+    id: int
+    task_id: int
+    path: str
+    note: str | None = None
+    station_id: int | None = None
+    device_code: str | None = None
+    acquired_at: datetime