Port the "Fluido" GPU fluid-simulation effect family from the Mac app

Verbatim engine copy (fluid.js + effects.js + visualizer.js) plus the
fluid.js script tag in output.html. 102 new audio-reactive ink-in-water
presets. Not yet deployed to the device (offline at commit time).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

public/output.html

@@ -31,6 +31,7 @@
   <script src="js/net.js"></script>
   <script src="js/engine/shaders.js"></script>
   <script src="js/engine/effects.js"></script>
+  <script src="js/engine/fluid.js"></script>
   <script src="js/engine/visualizer.js"></script>
   <script src="js/engine/audio.js"></script>
   <script src="js/output.js"></script>