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>

packages/server/test/media_endpoint_test.dart

@@ -54,9 +54,6 @@ void main() {
           resolveMediaRequest(rangeHeader: null, size: 10, filename: 'a.mkv', gate: MediaGate.unauthorized)
               .status,
           401);
-      expect(
-          resolveMediaRequest(rangeHeader: null, size: 10, filename: 'a.mkv', gate: MediaGate.forbidden).status,
-          403);
       final off =
           resolveMediaRequest(rangeHeader: null, size: 10, filename: 'a.mkv', gate: MediaGate.offline);
       expect(off.status, 503);