Creation of payment schedule needs exit/finish

There appears to be no way to specify a qty of payments, or for the payments to end after a date/period.

This means users are unable to establish such a payment schedule knowing that it finishes. As it appears to stand currently they only cease when either of two events occur:
1. The underlying lighting wallet sats run out - payment schedule has spent the bucket/budget OR
2. The payment schedule is manually cancelled - and we all know how easily recurrent payments get forgotten.

Running ZapPlanner under AlbyHub v1.13.0 on an Umbrel instance against an LND node.

No file, test, or entry point is named. Start by locating payment-schedule creation and the existing manual-cancellation flow, then determine how a payment count and an end date or period should be represented. Done means users can create schedules with either stopping condition and the schedule stops reliably without manual cancellation.

Written by the indexing model from the issue text.