Partner gift cards now settle automatically

Partner gift-card programmes now carry their money trail all the way through.
When a programme's agreement settles on sale, exporting its batch creates one
settlement entry per card. When it settles on redemption, using the card creates
the entry instead. Repeating an export or payment cannot duplicate what is owed.

The promises on cards already handed to a partner are now protected in the
database, not only in the edit form. Their value, currency, granted pass,
validity, batch and partner terms cannot be quietly rewritten after export.
Names, customer wording, dates and eligibility remain editable.

Pass gift cards generated from a programme now carry the selected pass's venue
price as their redeemable value. This fixes generated pass cards that could look
valid but be refused as empty when a client tried to claim them.

You can see the resulting totals in Gift Cards → Partner programmes → Settlement;
they continue into the same partner statement as promotion activity.