feat(site): drifting cloud puffs across the public background

Add a fixed, decorative layer of soft clouds that slowly float across
the Habbo sky behind the content:
- Five clouds at staggered sizes, heights, opacities and loop timings
  (60s–190s) so the drift feels organic.
- Dimmed further in dark mode; frozen by prefers-reduced-motion.
- Pure decoration: aria-hidden, pointer-events: none, no color
  utilities in markup (cloud shapes live in globals.css).

src/app/(site)/layout.tsx

@@ -1,5 +1,6 @@
 import dynamic from "next/dynamic";
 import type { ReactNode } from "react";
+import { CloudsField } from "@/components/clouds-field";
 import MotionPageWrapper from "@/components/motion-page-wrapper";
 import { Navigation } from "@/components/navigation";
 import { SiteFooter } from "@/components/site-footer";
@@ -29,6 +30,7 @@ export default async function SiteLayout({
 
 	return (
 		<>
+			<CloudsField />
 			{session?.user?.id ? (
 				<>
 					<div data-theme-block="top_header">