fix: set 3D spheres background to solid black on nthpartyfinder page

Restore solid dark CSS variables and set Three.js scene background to
black so the sphere effect renders against a black backdrop instead of
transparent/gray.

Generated with [Claude Code](https://claude.ai/code)
via [Happy](https://happy.engineering)

Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: Happy <yesreply@happy.engineering>

Author: 3 people

docs/projects/nthpartyfinder/index.html

@@ -22,10 +22,10 @@
    GRC Engineering colors + retro arcade aesthetic
    ══════════════════════════════════════════════ */
 :root {
-  --bg-deep:    transparent;
-  --bg:         transparent;
-  --bg-card:    rgba(17, 17, 40, 0.45);
-  --bg-surface: rgba(26, 26, 62, 0.45);
+  --bg-deep:    #06060f;
+  --bg:         #0b0b1a;
+  --bg-card:    #111128;
+  --bg-surface: #1a1a3e;
   --border:     rgba(255, 168, 79, 0.15);
   --border-hover: rgba(255, 168, 79, 0.5);
 
@@ -1076,6 +1076,7 @@ <h2 class="section-title">Ready to Find Your Nth Party?</h2>
 renderer.setPixelRatio(Math.min(window.devicePixelRatio, 2));
 
 const scene = new THREE.Scene();
+scene.background = new THREE.Color(0x000000);
 const camera = new THREE.PerspectiveCamera(50, 1, 0.1, 100);
 camera.position.set(0, 2.5, 5.5);
 camera.lookAt(0, 0, 0);