radiance: new home page — WebGL orb hero, DG cube loader, white dropdown menu

Replaces the Crush landing page with a single-screen hero (no scroll):
gradient sky, particle orb with corona, 'Welcome to dangrubb.net' title,
top-left DG logo and a numbered menu. Raw WebGL (no three.js), self-hosted
Instrument Sans + Geist Mono. ~10 KB of JS.

package.json

@@ -12,6 +12,8 @@
     "astro": "astro"
   },
   "dependencies": {
+    "@fontsource/geist-mono": "^5.3.0",
+    "@fontsource/instrument-sans": "^5.3.0",
     "astro": "^6.1.9"
   }
-}
+}