feat(site): make drifting clouds clearly visible and moving

The first cloud pass was to subtle: only five, up to 190s per crossing,
and they froze off-screen under prefers-reduced-motion. Rework:

- Eight clouds across the top 60% of the viewport with visible drift
  (28s–66s loops, staggered by negative delays so they are always mid
  scene on load).
- Higher opacity/steeper size contrast in light mode; dark mode dims
  them slightly.
- Reduced motion now freezes a static, evenly-spread cloud field across
  the width instead of pushing the clouds off-screen.

src/components/clouds-field.tsx

@@ -10,6 +10,9 @@ export function CloudsField() {
 			<span className="cloud cloud-3" />
 			<span className="cloud cloud-4" />
 			<span className="cloud cloud-5" />
+			<span className="cloud cloud-6" />
+			<span className="cloud cloud-7" />
+			<span className="cloud cloud-8" />
 		</div>
 	);
 }