FL-1268 add reservation detail read and check-level ticket fields for EOM migration
- pos.ReservationDetailReader (optional capability): GetReservation(ctx, id) fetches a single reservation incl. POS ticket line items, which the bulk export omits (FL-1339). sevenrooms implementation uses doWithRetry, maps HTTP 404 and envelope status 404 to pos.ErrReservationNotFound.
- pos.Ticket: add LocalPosTicketID, TableNo, StartTime, EndTime, EmployeeID, EmployeeName — needed by EOM's order and waiter sync flows.
- redact(): ticket-level staff identifiers are cleared from the audit RawPayload copy (typed DTO still carries them); the shared ticket slice is not mutated in place.
Co-Authored-By: Claude Fable 5 noreply@anthropic.com
Closes FL-1387