DX7 Import improved, Operator Phase, Operator descimation
Functional additions and fixes in this branch include:
- Per-operator start phase offset support in the synth engine.
- Operator phase marker visualization and editor/UI wiring for phase offsets.
- DX7 SysEx import hardening and mapping fixes (bank validation, vibrato/AMS handling, fixed-frequency preservation).
- FM decimation control added to engine parameters with preset/file persistence support.
- FM decimation expanded in oscillator DSP path to multiple domains: FM sum, phase increment/accumulator, phase modulation index/offset, waveform input, and oscillator output level before envelope multiply.
- High-quality wavetable interpolation is bypassed when decimation is enabled.
- bootloader unchanged and not tested
- rename binary to shorter name if necessary for SD card