README: add live demo link at the top

Make the live URL the first call-to-action on the repo page, before the
description and screenshot. Visitors land on the running demo with one
click rather than scrolling to the Deploy section.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: foxontheerun

README.md

@@ -1,5 +1,7 @@
 # Solar System — Real Newtonian Dynamics
 
+**→ Live demo: [foxontheerun.github.io/kam-solar-system](https://foxontheerun.github.io/kam-solar-system/)**
+
 Interactive 3D simulation of the Solar System with real planetary masses, distances, and Newtonian gravity. The KAM-stability panel lets you break stability by scaling masses, eccentricities, and orbital inclinations, or by applying gas drag.
 
 Built with [three.js](https://threejs.org/), no build step required.