WebGPU pixel look: GPU colours the world, CPU only rare cells (t88 phase 2a)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/ui/settings.js

@@ -16,6 +16,7 @@ const SET_TABS = {
     { k: 'shake', label: 'Screen shake', type: 'toggle' },
   ],
   Graphics: [
+    { k: 'renderer', label: 'Renderer', d: 'WebGPU colours the pixel look on the graphics card. Smooth uses the original renderer.', type: 'select', opts: [['webgpu', 'WebGPU'], ['legacy', 'Legacy']] },
     { k: 'look', label: 'Look', d: 'Smooth draws rounded, outlined ground, round grains and glossy liquids on the graphics card. Pixel is the original look, one square per grain.', type: 'select', opts: [['smooth', 'Smooth'], ['pixel', 'Pixel']] },
     { k: 'lighting', label: 'Lighting', d: 'Full is colored light at grain resolution. Fast uses half resolution.', type: 'select', opts: [['off', 'Off'], ['fast', 'Fast'], ['full', 'Full']] },
     { k: 'lightEvery', label: 'Light updates', type: 'select', opts: [[1, 'Every frame'], [2, 'Every 2nd frame'], [3, 'Every 3rd frame']] },