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/api/routers/vision.py

@@ -12,7 +12,9 @@ from src.backend.api.middleware.api_key import require_maker, require_measuremen
 from src.backend.api.routers.files import ALLOWED_IMAGE_TYPES, validate_file_size
 from src.backend.config import settings
 from src.backend.database import get_db
-from src.backend.models.api.vision import VisionExecuteResponse, VisionMeasurementResult
+from src.backend.models.api.vision import (
+    VisionExecuteResponse, VisionMeasurementResult, VisionReferenceImageResponse,
+)
 from src.backend.models.orm.task import RecipeTask
 from src.backend.models.orm.user import User
 from src.backend.services import vision_service
@@ -128,7 +130,7 @@ async def execute(
 
 
 # Composing a recipe and keeping a reference image are Maker operations, not
-# measuring: both endpoints below gate on `require_maker`, not the
+# measuring: every endpoint below gates on `require_maker`, not the
 # `require_measurement_tec` that `execute` above uses.
 
 
@@ -146,10 +148,39 @@ async def add_reference_image(
         db, task.id, content, note=note,
         extension=_IMAGE_EXTENSIONS[image.content_type],
     )
-    await db.commit()
+    try:
+        await db.commit()
+    except Exception:
+        # The row never became durable - the file `save_reference_image`
+        # wrote after its flush would otherwise outlive it as an orphan.
+        vision_service.remove_reference_file(reference)
+        raise
     return {"id": reference.id, "path": reference.path, "note": reference.note}
 
 
+@router.get("/reference-images", response_model=list[VisionReferenceImageResponse])
+async def get_reference_images(
+    task_id: int,
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(require_maker),
+) -> list[VisionReferenceImageResponse]:
+    await _task_or_404(db, task_id)
+    return await vision_service.list_reference_images(db, task_id)
+
+
+@router.delete("/reference-images/{reference_id}", status_code=204)
+async def delete_reference_image(
+    reference_id: int,
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(require_maker),
+) -> None:
+    reference = await vision_service.delete_reference_image(db, reference_id)
+    await db.commit()
+    # Only now: if the commit above had failed, the row would still exist and
+    # the file must still be there for it.
+    vision_service.remove_reference_file(reference)
+
+
 @router.post("/preview")
 async def preview(
     task_id: int = Form(...),