Bug: PedalApp._on_midi_cc() received (value, channel) where channel was
the MIDI channel (0-15) but was treated as the CC number (0-127). The
register_cc callback only passes value + MIDI channel, not the CC number.
Fix: Use a lambda closure in _wire_midi_callbacks to capture the CC
number so _on_midi_cc gets (value, cc_number, channel). Moved expression
pedal (CC#11) check before the presets/pipeline guard so it works even
when no preset is active.
Tests: 21 new integration tests covering:
- CC lambda closure capturing correct CC numbers
- Expression pedal → master volume (CC#11)
- Full parse→dispatch→callback chain for PC and CC
- Preset MIDI mapping lookup by CC number
- Edge cases: min/max values, rapid switching, empty slots
- Add JackAudioClient class to src/system/audio.py — real-time JACK
client owning ports and a process callback that streams audio through
the DSP pipeline. Handles mono (1ch I/O) and stereo 4CM (2ch I/O).
- Wire PedalApp.boot(): read audio.mode from config, set pipeline
routing_mode (mono/4cm), create and start JackAudioClient with
matching channel count.
- Add PedalApp.set_routing_mode(mode) — hot-switch between mono and
stereo_4cm at runtime: updates pipeline.routing_mode, restarts JACK
client with new channel count via set_channel_count(), re-connects
JACK ports.
- Wire shutdown: stop JackAudioClient before MIDI/footswitch.
- Export JackAudioClient from src.system.__init__.
- 53 tests pass (22 integration + 31 audio).
shawn