Add pegeongen.html: procedural pigeon plush generator

Self-contained single-page build of zlyfunction/PegeonGen. Generates Jellycat
Strutton-style plush pigeons from a seed using implicit surfaces (smooth-min
blended ellipse SDFs traced by radial ray marching) and procedurally derived
HSL palettes. No runtime dependencies.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: zlyfunction