Selling gift cards

Gift Cards live under the Products module — every Turtini org can issue, sell, and redeem them.

There are two concepts:

1. **Gift card products** (templates) — the design, denominations, and expiry policy. Each template publishes at /buy/gc/:productId with a printable QR.
2. **Issued cards** — a real bearer instrument with a unique TGC- code. Codes are minted server-side and stored in the public giftCardIndex collection so the recipient can check their balance at /redeem/:code.

To start selling:

1. Go to Gift Cards → Products → "+ New product"
2. Set denominations (e.g. $25, $50, $100) and optionally allow custom amounts
3. Toggle "Publicly buyable" on
4. Drop the Gift Card block on a Builder site (or share /buy/gc/:productId directly)

Public buyers pay through Stripe Checkout on your connected Stripe account — the cash flows directly to your org. The card is delivered by org-branded email with an "Add to Apple Wallet" button.

Accounting fan-out (when active):
- Issue: Cash 1010 debit / Gift Card Liability 2250 credit
- Redeem: Gift Card Liability 2250 debit / Sales Revenue 4800 credit
- Cancel/expire: Liability writeback (refund → cash, expire → revenue breakage)