Add inventory audit mode with camera QR scanning

Lets an employee walk the premises, scan each object's QR to confirm
it's present and record where it was found (defaulting to the last
picked location), and track found/not-found progress for the walk.
Scanning a box's QR shows its contents read-only without affecting
the found/not-found counts.

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

backend/app/services/objects.py

@@ -1,4 +1,5 @@
 import uuid
+from datetime import datetime, timezone
 
 from sqlalchemy import select
 from sqlalchemy.ext.asyncio import AsyncSession
@@ -20,6 +21,7 @@ def build_object_read(obj: InventoryObject) -> ObjectRead:
         box=BoxRef.model_validate(obj.box) if obj.box else None,
         created_at=obj.created_at,
         updated_at=obj.updated_at,
+        last_seen_at=obj.last_seen_at,
         qr_code_url=object_public_url(obj.id),
         photos=[build_photo_read(p) for p in obj.photos],
     )
@@ -62,6 +64,13 @@ async def update_object(db: AsyncSession, obj: InventoryObject, data: ObjectUpda
     return await get_object(db, obj.id)
 
 
+async def mark_object_found(db: AsyncSession, obj: InventoryObject, box_id: uuid.UUID | None) -> InventoryObject:
+    obj.box_id = box_id
+    obj.last_seen_at = datetime.now(timezone.utc)
+    await db.commit()
+    return await get_object(db, obj.id)
+
+
 async def delete_object(db: AsyncSession, minio_client, obj: InventoryObject) -> None:
     for photo in list(obj.photos):
         await delete_photo(db, minio_client, photo)