New 'Zona Effetto': each zone runs its own preset on an independent
offscreen Visualizer (960x540, own WebGL context), stepped with the
shared clock and audio so every panel dances to the same music with a
different effect (fluid presets included; interactive/3D excluded).
Zone row gains family/preset selectors; engines are created/destroyed
as zones change and their canvases uploaded as zone textures each
frame. Guide updated with the performance note.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
