Download Invoice for a booking

[harshtandiya]

The booking summary card in the My Calendar event drawer has room for a "Download Invoice" button, but there is nothing to download yet: the only Print Format in the app is standard_ticket, on Event Ticket.

What's needed

• A booking_invoice Print Format on Event Booking. Follow buzz/ticketing/print_format/standard_ticket/standard_ticket.json: custom_format: 1, print_format_type: Jinja, module: Ticketing, standard: Yes, pdf_generator: wkhtmltopdf.
• The body renders the booking number and date, the hosting team as issuer, the booking's tax_id and billing_address, the per-ticket-type breakdown with add-ons, and the totals ladder (subtotal, discount, tax, total).
• Surface the button in EventBookings.vue only when Event Booking.invoice_requested is set — that flag is what the booking form already collects alongside tax_id and billing_address.
• Link it the way dashboard/src/pages/TicketDetails.vue:23 links the ticket PDF, via frappe.utils.print_format.download_pdf.

Notes

Buzz User already holds print on Event Booking, and the permission query restricts a user to their own bookings, so no permission work is required.

The summary endpoint (buzz.api.booking.get_my_booking_summaries) deliberately omits invoice_requested; add the field to BookingSummary when this lands.