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>

docs/HOW-IT-WORKS.md

@@ -74,8 +74,10 @@ Friends join either way with Join in the strip at the top of the window.
    (stops blocking) and removed after 30 s. The app reconnects by itself and
    takes over your old place (same member, ready flag and video).
 
-There are no roles: anyone can seek, swap, force-ready others and kick
-anyone except the host.
+There are no roles: anyone can seek, swap, force-ready others, nudge
+anyone, and sit anyone out (the host too). Someone sitting out stays
+connected and in the chat, but their app loads nothing and nobody waits
+for them until they join back.
 
 ## Where video comes from