Adds a secondary Synth mode (toggled via collapsible left side panel)
where the NISPS ML engine's 20 outputs control curated C15 synthesizer
parameters (oscillator PM, shapers, filters, reverb, echo, flanger,
output mixer) through a WASM AudioWorklet bridge.
Includes a chord progression arpeggiator with controls for tempo (BPM),
octave range, octave offset, and 4 selectable progressions. The C15
engine runs in an AudioWorklet with lock-free SharedArrayBuffer ring
buffer communication.
New files: c15/ (WASM assets), js/synth/ (bridge, arpeggiator, param map),
serve-coop.py (COOP/COEP headers for SharedArrayBuffer support).
