Store when barcode was last scanned

Groceries.Data/Migrations/20241005180119_item_barcodes_last_scanned_at.sql

@@ -0,0 +1,7 @@
+ALTER TABLE item_barcodes
+ADD COLUMN IF NOT EXISTS last_scanned_at timestamptz NOT NULL DEFAULT current_timestamp;
+
+UPDATE item_barcodes
+SET last_scanned_at = created_at
+FROM item_purchases
+WHERE item_barcodes.item_id = item_purchases.item_id AND is_last_purchase = true;