fix(landing): merge the final scene's two suns into one

The closing sky drew two suns: the 3D sun mesh (corona + GodRays) at a
fixed world point, and a disc/halo painted by the sky shader aimed at a
fixed direction. As the camera flew forward, parallax split them apart —
the mesh rode high while the painted halo stayed low.

Aim the sky shader's uSunDir at the real camera→sun direction each frame
so the halo locks onto the mesh (one sun), and lower SUN_POS.y 34→13 so
that single sun sits at the lower, near-horizon spot.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/components/landing/SceneCanvas.tsx

@@ -15,7 +15,7 @@ import { rainVertexShader, rainFragmentShader, skyVertexShader, skyFragmentShade
 // <WeatherClock/> (mounted first) and read by every other piece of the scene.
 const weather = makeWeatherSample();
 
-const SUN_POS = new THREE.Vector3(0, 34, -205);
+const SUN_POS = new THREE.Vector3(0, 13, -205);
 const SKY_RADIUS = 400;
 
 function WeatherClock() {
@@ -49,6 +49,10 @@ function GradientSky() {
     m.uniforms.uSunColor.value.copy(weather.sunColor);
     m.uniforms.uSunReveal.value = weather.sunReveal;
     m.uniforms.uCameraPos.value.copy(state.camera.position);
+    // Aim the painted sky-sun along the real camera→sun direction so its halo
+    // stays locked onto the 3D sun mesh. Using a fixed direction made it drift
+    // into a second, lower disc as the camera flew forward (parallax).
+    m.uniforms.uSunDir.value.subVectors(SUN_POS, state.camera.position);
     if (meshRef.current) {
       meshRef.current.position.x = state.camera.position.x;
       meshRef.current.position.z = state.camera.position.z;