docs(call): cover soundboard/quality/permissions in user-facing docs

- README "Calls & Voice": add the in-call soundboard, per-user call quality
  settings, and admin room call-permissions bullets.
- LOTUS_TODO: mark the soundboard UI as built (was "cinny UI remains / dormant").
- HANDOFF_ELEMENT_CALL_FORK: add a COMPLETE status banner to the §12.1 host
  checklist; fix stale denoise specifics (all four models are in-source;
  flag is lotusDenoiseSource=1, not lotusDenoise=ml).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

README.md

@@ -52,6 +52,9 @@ The Lotus Chat logo (`public/res/Lotus.png`) is a derivative work based on the o
 - AFK auto-mute: mic is automatically silenced after a configurable idle timeout (1–30 min); a toast confirms the action
 - Voice channel user limit: admins can cap how many people can be in a room's call — enforced server-side for every Matrix client (not just Lotus Chat); others see "Channel Full" until a spot opens
 - Custom join/leave sound effects when someone enters or leaves your call — choose Chime, Soft, Retro, or off
+- Soundboard: upload your own short audio clips (like custom emojis — they sync across your devices) and play them into a call so everyone hears them
+- Call quality settings: cap your microphone bitrate, screenshare bitrate, and screenshare framerate — handy on a slow connection (Settings → Calls)
+- Room call permissions: admins can turn off screen sharing or make a room audio-only (no cameras) — enforced server-side for every Matrix client, and it stops an in-progress share within seconds of being switched off
 
 ### Customization & Appearance