Server-side: add DB persistence for voice restrictions (schema, migration,
ready payload, cleanup on leave). Client-side: fix four bugs that wiped or
bypassed server restriction state — leaveVoice() no longer clears global
restriction Sets, voice_state_update leave no longer drops amber icons,
toggleMic/toggleDeafen now guard against server restrictions, and force-mute/
deafen uses direct setState instead of fragile toggle calls.