add reward card feature with barcodes

src/domain.rs

@@ -113,3 +113,19 @@ pub struct PresenceUser {
     pub user_id: i64,
     pub display_name: String,
 }
+
+/// A stored rewards-card number that can be shown as a scannable barcode.
+#[derive(Clone, Debug)]
+pub struct RewardsCard {
+    pub id: i64,
+    /// The owner of this card.
+    #[allow(dead_code)]
+    pub user_id: i64,
+    pub store_name: String,
+    pub number: String,
+    /// Symbology used to render the barcode (e.g. "code128", "code39").
+    pub symbology: String,
+    /// When the card was added.
+    #[allow(dead_code)]
+    pub created_at: i64,
+}