fix(listen): include reply metadata in --json output

`hcom listen --json` emitted only from/text, so a machine consumer could
not build `send --intent ack --reply-to <id>`. Both listen paths now emit
event_id, reply_id, intent and thread.

reply_id is what `--reply-to` accepts: the local event id, or
`<origin_id>:<DEVICE>` for relay-imported messages, matching what hook
delivery shows. A local id is meaningless on the sender's device, and
reply_to is relayed as written. Text-mode listen and hookless
(adhoc/codex) command output used the local id for relayed messages;
they now use the same reply id.

Replaces `Message.relay`, which was always false (`_relay` is an
object), with `relay_ref` and `Message::reply_id()`.

Refs #118