Zaubertopf discount tokens

Issues one discount token per day and keeps the shop's hash list in sync, so the cart discount only applies to carts that carry a current token.

• One token per day. Created automatically at midnight, or on demand through the API.
• Valid for 48 to 49 hours. The shop metafield lists every token that has not aged out yet.
• Club members excluded. Customers tagged CLUBMITGLIED already get their membership price.