Adds an audio_gain_boost_enabled status column (plus _at/_by audit
fields) to user_status, exposed as user.audioGainBoost and copied onto
sockets as socket.data.hasAudioGainBoost. The flag marks VIPs allowed to
raise their personal horn/TTS/mic gain ceiling past the global admin gain
settings.
Grant/revoke goes through verificationService so socket flags refresh and
an event is published. Resolution is restricted to verified users, so an
unverified visitor sharing a nickname can never be matched.
Co-Authored-By: Claude <noreply@anthropic.com>
