fix(collection-map): clear assigned_at on unassign so item returns to pool

src/app/api/v1/collection-map/items/[id]/assign/route.ts

@@ -97,6 +97,15 @@ export async function PATCH(
         patch.notes = readyNotes;
       }
     }
+    // Returning an item to the pool (no driver being assigned) also
+    // clears the date the operator originally assigned. Without this,
+    // the item keeps its old `assigned_at` and the collection map's
+    // date filter (which matches by string compare on `assigned_at`)
+    // may still surface it under the wrong day, or hide it entirely
+    // on the un-dated fallback.
+    if (!isAssigning) {
+      patch.assigned_at = "";
+    }
 
     const pb = await getAdminPocketBase();
     const current = await pb.collection(getOrderItemsCollectionName()).getOne(id).catch(() => null);