Add Spiral goo animation: separate file with customizable spinning spiral gradient

[curtisahuang]

Introduced a new spiral goo animation as a standalone file and wired it into the playground for modularization and reuse. The spiral gradient spins and unwinds into straight arms, leaving a liquid-like trail, with the base color and disturbance color controlled by the user.

What changed:

• assets/animation-spiral-liquid.js (new): Added createSpiralLiquidProject which renders a rotating spiral that straightens out. It supports gradient coloring, a straight unwind path, and a trailing effect. Controls include primaryColor, secondaryColor, spinSpeed, spinDuration, shape (spokes, triangle, square), and thickness/softness for the liquid feel. When using spokes, you can adjust the number of spokes. The code uses offscreen rendering for performance and applies a gradient stroke to arms drawn around a rotation.
• assets/main.js: Imported the new spiral module and added it to the list of available projects so it appears in the playground.
• assets/style.css: Minor adjustments to control styling to accommodate new controls (select styling for consistent appearance).

How this solves the task:

• The fourth animation is now modularized in its own file, making it easier to maintain and swap in. The spiral gradient can spin and unwind, with a trail that mimics liquid dynamics. Users can tune colors, spin speed, and unwind duration, and switch shapes or the number of spokes to alter the spinning form.

https://cosine.wtf/cosine-stg/animation-playground/task/vc01u7ggguh2
https://cosine.wtf/gh/CosineAI/animation-playground/pull/4
Author: Curtis Huang