bfe1434f75
- Channel enum (GUITAR, BASS) with channel field on Preset dataclass
- Channel-prefixed storage: {root}/{channel}/bank_{bank}/preset_{program}.json
- PresetManager channel awareness: set_channel(), current_channel property
- Per-channel state persistence (channel_state.json per channel dir)
- Legacy migration: flat bank_* dirs auto-migrate to guitar/ on first boot
- All CRUD methods accept optional channel parameter
- API endpoints accept channel param on GET/PUT/DELETE /api/presets
- /api/channel GET/POST for channel switching
- 10 new channel tests (independence, switching, migration, scoping)
- Factory presets install to specified channel