feat(call): in-call soundboard, quality controls, room call-permissions

Element Call is now consumed as our self-built fork
(@lotusguild/element-call-embedded); wire up its previously-dormant
capabilities and document the fork as live.

Soundboard (P5-15): a call-bar button plays user-uploaded audio clips into the
call as a real published track (io.lotus.inject_audio) plus local playback.
Clips are uploadable like emoji/sticker packs, stored in io.lotus.soundboard
account data (synced across devices). Gated by a Settings toggle + volume.

Quality controls (P5-31): per-user mic/screenshare bitrate + screenshare
framerate (Settings -> Calls), applied via io.lotus.set_quality clamped to any
room cap. Room admins set caps and hard call-permissions (allow_screenshare /
allow_camera) in Room Settings -> Voice; the call bar hides blocked buttons.

- New: CallSoundboard, useSoundboard, soundboardClips; RoomQuality,
  useCallQuality, callQuality (+ unit tests).
- Optimistic-write RoomQuality admin UI (no stale-state clobber).
- Docs: mark EC fork live across README/FEATURES/TODO/BUGS/TESTING; add D2
  manual-test steps.

Numeric quality caps are client-cooperative; screenshare/camera permissions are
hard-enforced server-side (see LotusGuild/matrix voice-limit-guard).

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

src/app/plugins/call/CallEmbed.ts

@@ -179,6 +179,11 @@ export class CallEmbed {
       //  - transparent background so the room wallpaper shows through natively
       lotusCallState: 'true',
       lotusTransparent: 'true',
+      // [lotus #3 / P5-15] Arm the fork's audio-inject handler so the in-call
+      // soundboard can publish clips into the call. Dormant until the host
+      // sends io.lotus.inject_audio (only on an explicit user click), so
+      // arming it for every call is safe.
+      lotusAudioInject: 'true',
     });
 
     if (denoiseMode === 'ml') {