Restructure step 1: lasting identity, presence and protocol 16

Server and core: version ranges on both sides with a coded refusal; a
client id maps to the same member and token for the server's life; a
drop is `gone` for a 10-minute grace keeping ready, presence, queue
items, relay and avatar; `bye` leaves at once; ordered takeover (seq,
replaced/stale); presence joining/in/away/gone with one PresencePolicy;
joiners never pause playback and hold a held gate at most ~15 s;
state.hold; feed ids, seq and replay; the relay lives through its
source's grace and continues on re-dial; queue `by` lasting, auto
items and cancel; MediaRef carried; client ids never logged.

App: persisted client id and seq; Connection with unstable/lost/
replaced states, backoff with jitter, no lost/back pair per flap; a drop
keeps the session (state, player, media, relay source); presence in the
strip and members card; sit out = away intent; feed matched by id;
auto sit-out (idle when not playing, minimised for a while; never when
alone) replaces auto-unready; bye on close and Leave, not on update
restart; relay source re-dials through its grace.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/desktop/lib/src/shell/toasts.dart

@@ -80,7 +80,7 @@ class _PartyToastsState extends State<PartyToasts> {
         final playing = coord.serverState.value?.transport == 'playing';
         final popups = AppSettings.instance.chatPopups.value;
         for (final t in fresh) {
-          final toast = shellToastFor(t, (n) => avatarForName(n, coord));
+          final toast = shellToastFor(t, (n) => avatarForName(n, coord, t.actorId));
           // Chat per Settings → Notifications (it is in the chat either way).
           if (toast.chat && !popups.shows(playing: playing)) continue;
           _add(toast);