The app previously showed 'Gateway restarting' on every connection loss.
Now the gateway broadcasts status{state=restarting} on its shutdown path
(before closing the sockets), and the app:
- posts 'Gateway restarting' immediately on that frame (not on the
socket-drop transition, which lags by the ~20s WS ping timeout)
- posts 'Gateway online' on the next reconnect only when the restart
notice was posted (latch) - a plain network drop shows neither, just
the reconnect banner
- drops the 'Gateway is restarting...' banner (replaced by the chat notice)
Docs (04-wire-protocol, frames.schema.json) updated: restarting is no
longer reserved. Test for the disconnect broadcast added to the local
hermes-agent test mirror (git-ignored, not committed).