[VIZ] Implement Instanced Volumetric Caustics and Depth-of-Field in 3D Danionella Chamber

[0xalydev]

Summary

The new 3D Danionella whole-organism hero visualization (web/hero_organism.js) renders an adult teleost fish with transparent optical skin and an internal 203-region brain. To push the visual fidelity to high-end scientific imaging standards (mimicking deep-tissue two-photon microscopy), we want to add an optional volumetric lighting / caustics post-processing pass.

Feature Specifications

1. Volumetric Caustics Shader:
   • Subtle animated underwater light refraction caustic rays projected into the dark chamber void.
   • Low GPU overhead using a procedural simplex noise lookup in a fullscreen quad.
2. Depth-of-Field (Bokeh DoF):
   • Subtle camera focus on the cranial optical aperture ($Z \approx 0$).
   • Soft background blur on the undulating caudal tail fin.
3. Performance Toggle:
   • Add a [⚡ POST-PROCESSING: ON/OFF] button in the HUD controls to preserve 60 FPS on low-power mobile/integrated GPUs.

Key Files

• web/hero_organism.js: Hero WebGL simulation class.
• web/danio_webgl_brain.js: Connectome WebGL renderer.
• web/style.css: HUD dock styles.

Acceptance Criteria

• Caustics and DoF render without visual artifacts.
• Desktop performance maintains $\ge 55$ FPS on integrated GPUs when enabled.
• Toggle switch gracefully enables/disables the post-processing pass.