New files:
- MixerApi.hpp/cpp: Model-level API bridging WebSocket messages to
MixerEngine control (channel volume/pan/mute/solo/hpf, bus control,
routing, state queries)
- 15 new WebSocket message handlers in PiPedalSocket.cpp for full
mixer control surface
Integration:
- MixerEngine member added to PiPedalModel with Get/Set accessors
- SetMixerEngine propagates to AudioHost rt processing pipeline
- Socket handler auto-wires MixerEngine to MixerApi on connect
Messages implemented:
mixerSetChannelVolume, mixerSetChannelPan, mixerSetChannelMute,
mixerSetChannelSolo, mixerSetChannelLabel, mixerSetChannelHpf,
mixerGetState, mixerAddChannel, mixerRemoveChannel,
mixerSetBusVolume, mixerSetBusMute, mixerAddBus, mixerRemoveBus,
mixerRouteChannelToBus
shawn