Adds group context fields to MessageSentHookContext so hooks can
correlate sent events with received events for the same conversation.
Previously, message:received included isGroup/groupId but message:sent
did not, forcing hooks to use mismatched identifiers (e.g. groupId vs
numeric chat ID) when tracking conversations.
Fields are derived from MsgContext in dispatch-from-config and threaded
through route-reply and deliver via the mirror parameter.
Addresses feedback from matskevich (production user, 550+ events)
reported on PR #6797.
b5102ba4f9