style: mute nebula intensity, fix load visibility, and sync parallax

apps/web/src/components/landing/dynamic-background.tsx

@@ -6,6 +6,13 @@ import { useEffect, useState } from "react";
 
 export function DynamicBackground() {
   const { theme } = useTheme();
+  const [mounted, setMounted] = useState(false);
+
+  useEffect(() => {
+    setMounted(true);
+  }, []);
+
+  if (!mounted) return null;
 
   return (
     <NebulaField