Replace box picker with free-text location in audit scan

"Where found" during inventory audit is now a plain text field
(e.g. "каб. 305") stored on the object instead of assigning it to a
box, since audit walks often use room/office labels that don't map
to the box/shelf hierarchy used elsewhere. Box assignment via the
regular object form is unaffected.

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

backend/app/services/objects.py

@@ -22,6 +22,7 @@ def build_object_read(obj: InventoryObject) -> ObjectRead:
         created_at=obj.created_at,
         updated_at=obj.updated_at,
         last_seen_at=obj.last_seen_at,
+        last_seen_location=obj.last_seen_location,
         qr_code_url=object_public_url(obj.id),
         photos=[build_photo_read(p) for p in obj.photos],
     )
@@ -64,8 +65,8 @@ 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
+async def mark_object_found(db: AsyncSession, obj: InventoryObject, location: str | None) -> InventoryObject:
+    obj.last_seen_location = location
     obj.last_seen_at = datetime.now(timezone.utc)
     await db.commit()
     return await get_object(db, obj.id)