Sounds: Japanese-house sound set in the app, layout demo removed

Eleven sounds for events that carry news (ready, unready, everyone ready,
join, leave, kick, new video, others' chat, idle warning, connection
lost/back); none for what the video already says. New voices: koto
(Karplus-Strong, bendable), furin chime, rin bowl, bamboo, hyoshigi,
shoji slide, in the Yo scale on D. Played by SynthSfx at the Settings
volume with per-sound switches and previews. The debug layout mock is
gone.

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

README.md

@@ -149,8 +149,8 @@ of help: Profile; Party & network (the Host card's default port and
 password, recent servers with remove); Player (below); Jellyfin &
 integrations (linked Jellyfin servers, below, the AnimeFlow connection:
 "connected as <name>" with what you may do, or why not, and playing the
-next episode automatically); Notifications & sounds (what pops up; there
-is nothing to switch yet); Updates; Keyboard shortcuts (read-only); About
+next episode automatically); Notifications & sounds (what pops up; the sound
+volume, and every sound with a preview and its own switch); Updates; Keyboard shortcuts (read-only); About
 (the version).
 
 Player settings live in the player: ⚙ at the right end of its controls