- App.tsx: Import and render MetersPage when 'Meters' button toggled;
add Meters button to header between Patch and PiPedal buttons
- useMixerDaemon.ts: Add gateOpen and compressorReduction fields to
MixerChannel interface
- MetersPage.tsx: Add gate open/closed indicator (green/red G badge)
and compressor gain reduction bar to ChannelMeterTile
- MetersPage.css: Add gate indicator and compressor GR track styles
