Leg 0.16.3: Checkout delivers keys for delayed payments, and Team keys carry today's seats

Checkout delivers keys for delayed payments, and Team keys carry today's seats.

• A Personal purchase paid by bank debit completes checkout unpaid. Its key is
  now emailed when Stripe confirms the payment
  (checkout.session.async_payment_succeeded), after the session is read back
  from Stripe and checked as paid and as the Personal price. Unpaid and failed
  payments still get no key, and a replayed or out-of-order event sends one key.
• A Team key from the checkout link, leg license refresh or a renewal now
  reads its seats and period from the subscription's current Leg Team item,
  so reopening an old checkout link after a seat change no longer signs the
  original seat count. A seat count that is not a positive whole number, or a
  subscription with two Team items, gets no key.
• The thanks page no longer says the key "went to" your email: the page shows
  the key it fetched and says it cannot confirm the emailed copy. When the
  key cannot be fetched yet, it explains the bank-debit wait and where to write.
• scripts/stripe-setup.mjs subscribes the webhook to the delayed-payment
  event, and adds it to an existing endpoint without dropping the others.