Protocol 11: sit out replaces kicking; nudge

Anyone can sit anyone out (host included); only you bring yourself back.
Out members stay in chat and the party, never block or count, and load no
media; a card with the live position and Join back (Space) replaces the
video. The mini player's x sits you out; optionally idle does too. Nudge:
the server forwards it to the target only (3/s, 20/min per sender); the
target hears the nudge sound, gets a toast and a taskbar attention
request. Kick, its messages, errors and dialog are gone.

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

apps/desktop/lib/src/sfx/sfx.dart

@@ -8,6 +8,7 @@ enum SfxKind {
   forceReady,
   join,
   leave,
+  /// Someone sat you out (played by the session, not from a feed action).
   kick,
   /// A new video or episode is put up.
   swap,
@@ -31,7 +32,6 @@ SfxKind? sfxForFeedAction(String action) => switch (action) {
       'ready' => SfxKind.ready,
       'unready' => SfxKind.unready,
       'force-ready' => SfxKind.forceReady,
-      'kick' => SfxKind.kick,
       'join' => SfxKind.join,
       'leave' => SfxKind.leave,
       'swap' => SfxKind.swap,