Pass `currency` to Stripe checkout for first-time buyers so Stripe
picks the matching `currency_options` rate configured on the Price
in the Dashboard (multi-currency Prices: one Price, per-currency
unit_amount). Operator configures the rates on existing Prices
prod_UaZ0xCpCboUGCN/price_*; this commit is the application-side
signal.
Currency precedence: explicit request body > Cloudflare cf-ipcountry
header > Accept-Language locale > GBP fallback. Only honoured when
the user has no stripe_customer_id yet — Stripe locks currency to
the customer record at first checkout, so existing customers keep
their original currency (they can switch via the portal).
Adds 4 tests: sniffed currency on new customer, body override beats
sniff, currency omitted for existing customer, and unit-tests for
the sniffing fallback chain.
Giorgio Gilestro
83995e96c8