feat: Add promotion code functionality to ticket orders

db/migrate/20250928181311_create_order_promotion_codes.rb

@@ -0,0 +1,10 @@
+class CreateOrderPromotionCodes < ActiveRecord::Migration[8.0]
+  def change
+    create_table :order_promotion_codes do |t|
+      t.references :order, null: false, foreign_key: true
+      t.references :promotion_code, null: false, foreign_key: true
+
+      t.timestamps
+    end
+  end
+end