Easy!Appointments re-fires appointment_save on reschedule with the same
EA-<id> booking_id, so add_entity's plain INSERT 500s on the PK conflict.
Switch to ON CONFLICT (pk) DO UPDATE for every entity except activity_log
(no client-supplied pk), logging add vs update accordingly. Extended to
all keyed entities per the issue body, while preserving created_at/
received_at on redelivery for leads/clients/credentials so a redelivered
webhook can't clobber the original creation time.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
