When reacting to WhatsApp group messages, the 'participant' field is
required by Baileys but was previously optional, leading to silent
failures where reactions appeared to succeed but were never sent.
This change adds validation to fail fast with a clear error message
when attempting to react to a group message without providing the
participant JID.
Fixes issue where reactions in WhatsApp groups returned {ok: true}
but were never delivered to WhatsApp servers.
Example error:
WhatsApp group reactions require the 'participant' field (sender JID).
Example: participant: '1234567890@s.whatsapp.net'
