- Channels 0-1 are now dedicated Mic 1/Mic 2 with mic_on toggle
- Mic audio only routes to main when mic_on=True, never to headphone
- New headphone_out_L/R JACK ports (all channels except mics)
- New studio_out_L/R JACK ports (copies main, mutes when any mic is on)
- Mic ON/OFF toggle button in mixer UI (hidden on non-mic channels)
- Session save/load includes mic_on state
TopBarWidget already connects mapping_learned to _on_mapping_learned internally
in set_midi_engine, so the external connection in main.py was both redundant
and referenced a non-existent method.