Add interactive 3D sinusoidal spiral with particle flow (8-period limit)

[curtisahuang]

This PR introduces a new 3D spiral visualization with interactive camera controls and particle motion, and wires it into the existing project system.

What changed

• Added assets/animation-spiral-3d.js

  • Renders a sinusoidal 3D spiral that is visually bound by 8 periods to prevent unbounded distances.
  • Precomputes the spiral path and populates particles that travel along the line with varied speeds, sizes, and colors.
  • Implements a camera system (orbit and pan) with mouse interactions: drag to rotate, right-click/ctrl/shift-drag (or equivalent) to pan, and mouse wheel to zoom.
  • Uses a simple perspective projection with per-point depth handling and alpha/size modulation to convey depth.
  • The spiral uses a base radius, wobble, and frequency settings tuned for a pleasing 3D look while keeping everything within a reasonable distance.

• Added assets/animation-starfield.js

  • Lightweight starfield background to complement the new 3D spiral, providing parallax and ambient motion.
  • Responds to pointer events for a subtle parallax effect and updates each frame.

• Updated assets/main.js

  • Imported and registered the new starfield and spiral-3d projects.
  • Added createStarfieldProject and createSpiral3dProject to the environment so they appear as additional tabs (including the new fifth tab scenario).

How this solves the issue

• Provides a fifth-tab-ready 3D sinusoidal spiral visualization that users can rotate, pan, and zoom with the mouse.
• Renders a finite spiral by capping to about 8 periods, ensuring the scene remains performant and visually contained.
• Adds dynamic particles with varied sizes and speeds that travel along the spiral for a more engaging visualization.
• Integrates seamlessly with the existing project system, keeping behavior consistent with other animations in the app.

https://cosine.sh/cosine/animation-playground/task/52ezj7p2jom9
https://cosine.sh/gh/CosineAI/animation-playground/pull/5
Author: Curtis Huang