The historical-invoice import form had no event field, so imported rows
landed with event_name = NULL even when the admin knew the occasion. Add
free-text Event name + Event date inputs to the import modal, thread them
through billsService.importHistorical and the POST /admin/invoices/import
validator, and store them in the event_name/event_date snapshot columns
(migration 107). event_id stays NULL — no FK, since the event may predate
picpeak. Autocomplete-to-event_id linking deferred as a future bonus.
Luca
db7d11dc7f