Booking a slot with no priced offering created the lesson but no payment,
yet the front end still called POST /payments/intent, which 400ed with
"Could not start payment for this registration" — the student saw an error
while the backend held a claimed slot and a lesson stuck at pending.
- POST /bookings and POST /enrollments now return a `payment` summary
({id, method, status}) or null when nothing is owed; the JS only runs
the payment step when a payment exists.
- Bookings with nothing owed are confirmed at creation — there is no
payment step that would ever confirm them later.
- The booking page now shows the student's upcoming lessons (GET /bookings,
now scoped to upcoming non-cancelled lessons with slot start/end times)
with a pending-payment/confirmed status badge.
Fixes#53
Co-Authored-By: Claude Fable 5 <[email protected]>
