Adds 2 new models for grand-finale logistics PR 2:
- Hotel: 1:1 with Program (one per edition); name + address + link + notes
- FlightDetail: 1:1 with AttendingMember; arrival + departure datetimes,
flight numbers, airports, admin status (PENDING/CONFIRMED), admin notes
Migration is purely additive: no DROP/ALTER COLUMN/RENAME. FKs point
FROM new tables TO existing tables (Program, AttendingMember) with
ON DELETE CASCADE only firing on parent deletion.
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