Switches the synth from monotimbral AVAudioUnitSampler to multi-timbral AVAudioUnitMIDIInstrument backed by Apple's MIDISynth. All 128 GM programs + the drum kit are pre-loaded on boot via kAUMIDISynthProperty_EnablePreload, so dragging across the instrument grid triggers instant program changes (MIDI Program Change events instead of ~100 ms bank reloads). Other fixes in this build: - Octave widget pinned to the popover's top-left; MIDI pair stays right. - Lit-state on the menubar piano: minVisibleSeconds bumped to 180 ms and startTapNote updates litNotes synchronously when called on the main thread so the blink shows during the click drag-loop. - AppDelegate.updateIcon now forces a synchronous redraw so hover and lit highlights show up inside event-tracking mode (the runloop wasn't flushing CATransactions until mouseUp). - WaveformView: coalesce CVDisplayLink callbacks (drop backed-up frames), wrap path swap in a no-action CATransaction, slightly snappier auto-gain. - Landing page: cache-bust to ?v=bf4a2f8 for the new DMG.