feat: add reactbits splash-cursor (WebGL fluid simulation)

[ResourceMint]

What does this PR do?

Add a splash-cursor showpiece entry: ReactBits' WebGL fluid-simulation cursor effect.

Type

• New component entry

Checklist

• components.json is valid JSON (CI will verify).
• Each new/changed ref was tested on a fresh React + Tailwind project.
• ref uses the full registry URL form (https://reactbits.dev/r/SplashCursor-TS-TW), verified to return a registry:component JSON item (not the HTML shell).
• license is filled in and correct (MIT, ReactBits).
• No duplicate of an existing entry (checked names + aliases; closest existing are aurora and wavy-background, both distinct backgrounds, not a cursor-driven fluid sim).

Notes

• Self-contained WebGL2, zero npm deps (deps: []), so it drops into any React + Tailwind project with no extra install.
• Fills a real gap: the registry had no fluid-simulation / liquid-cursor effect. Aliases cover "fluid cursor", "fluid simulation", "fluid motion", "liquid cursor", "navier-stokes fluid".
• Adaptation at use time still applies (brand-token colors + prefers-reduced-motion), per the skill rules.