feat: Add promotion code functionality to ticket orders

db/migrate/20250928180837_create_promotion_codes.rb

@@ -0,0 +1,16 @@
+class CreatePromotionCodes < ActiveRecord::Migration[8.0]
+  def change
+    create_table :promotion_codes do |t|
+      t.string :code, null: false, unique: true
+      t.integer :discount_amount_cents, null: false, default: 0
+      t.datetime :expires_at
+      t.boolean :active, default: true, null: false
+      t.integer :usage_limit, default: nil
+      t.integer :uses_count, default: 0, null: false
+      t.datetime :created_at, null: false
+      t.datetime :updated_at, null: false
+    end
+
+    add_index :promotion_codes, :code, unique: true
+  end
+end

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