Liquid Shader Field

# Liquid Shader Field — WebGL Animated Background

## Goal
Build a full-section animated background driven by a single fragment shader: layered simplex noise warping three colour stops into a slow liquid flow, with a gentle pointer-driven ripple. It must drop cleanly into an existing Next.js + Tailwind project as a self-contained component.

## Design Spec
- One full-size canvas, `position: absolute; inset: 0; z-index: -1`, behind arbitrary content.
- Shader takes three uniform colours plus `uTime`, `uPointer` (vec2, normalised) and `uIntensity`.
- Colour mixing happens in linear space and con