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/schemas/object.py

@@ -36,7 +36,7 @@ class ObjectUpdate(BaseModel):
 
 
 class ObjectScan(BaseModel):
-    box_id: uuid.UUID | None = None
+    location: str | None = None
 
 
 class ObjectRead(BaseModel):
@@ -51,5 +51,6 @@ class ObjectRead(BaseModel):
     created_at: datetime
     updated_at: datetime
     last_seen_at: datetime | None
+    last_seen_location: str | None
     qr_code_url: str
     photos: list[PhotoRead]