Use solo piano optimizer for full-song melodic stem, reduce LH bass notes

Fix MetalSynth API (HH/ride/crash) and use mix audio for beat tracking

Fix piano roll quality, drum sounds, add original audio playback, fix speed

Add drum transcription with madmom onset detection + spectral classification

Remove unused vocal transcription and arrangement from full song pipeline

Use direct melodic transcription for piano roll instead of arrangement

Full Song quality pass: light optimizer, better guitar sound, tab accuracy

Add piano arrangement engine + guitar/bass tab views for Full Song mode

Add Full Song mode with Demucs source separation

Initial commit - Mr Octopus piano tutorial app