Optimize WebXR frame workload for Quest

[reality2-roycdavies]

Summary

• Cache procedural minimap terrain and render only the active desktop/VR display.
• Simulate rain and snow analytically on the GPU, replacing the 5,000-particle CPU update and per-frame buffer uploads.
• Skip disabled foam generation during full-detail chunk builds.
• Version the changed browser modules for a fresh headset load.

Validation

• npm test: 203 tests passed.
• Modified JavaScript passes node --check.
• Rain/snow vertex and fragment shaders pass glslangValidator.
• The local browser resolved the complete versioned module graph. This container blocks headless WebGL2, so final runtime validation is on Quest via GitHub Pages.

Deployment

GitHub Pages serves main at https://reality2-roycdavies.github.io/vr-forest/. Merge after CI publishes the headset build.