Beam Grid Horizon

# Beam Grid Horizon — Animated Background

## Goal
Build a perspective 'floor grid + horizon glow + traveling beams' background for dark hero sections. It must drop cleanly into an existing Next.js + Tailwind project as a self-contained component.

## Design Spec
- Floor: a div rotated with perspective (rotateX ~60°) carrying a repeating-linear-gradient grid (1px lines, 40px cells, cyan at 12%), masked to fade before the horizon line.
- Horizon: a 2px glowing line (accent color, blur + brighter core) across the section at ~38% height, with a radial glow bloom behind it.
- Beams: 3 vertical lig