Refund and class-message workflows completed

Refunds now use the same focused dialog from client Billing, POS, Daily Sales,
and payment details. The dialog supports partial refunds, defaults to the
original payment method (including the card brand and last four digits), offers
the venue's other active refund methods, and can send receipts by email, text,
push, or print when each channel is available.

Daily Sales no longer sends staff to a separate refund page. The refund opens
over the sales drawer and the figures refresh after completion.

When several schedule classes are selected, staff can now choose email, SMS,
or both; send immediately or at a venue-local date and time; and keep sending
to clients who book later. Open scheduled and follow-on messages are shown in
the same window and can be cancelled there. Recipients shared across selected
classes are deduplicated.