More clouds + finer structure, switch default back to clouds3d

- WEATHER_DENSITY bumped: sunny 0.20->0.55, cloudy 0.70->0.85,
  night 0.45->0.65. Stormy stays at 1.0 (already maxed).
  Even 'sunny' now has visible cloud structure, not just clear sky.
- clouds3d: add a second fBm layer at 4x frequency for fine detail,
  blended at 18% into the base. Combined with the tighter smoothstep
  (0.24 -> 0.18) the cloud silhouettes have more interesting edges
  instead of soft blob shapes.
- Same density bump applied to clouds2d so swapping renderers
  doesn't change the visual weather.
- config.renderer: clouds2d -> clouds3d (user request)

config.js

@@ -46,7 +46,7 @@ window.CONFIG = {
     units: {
         temperature: 'C'
     },
-    renderer: 'clouds2d',  // 'vanta', 'clouds2d', or 'clouds3d'
+    renderer: 'clouds3d',  // 'vanta', 'clouds2d', or 'clouds3d'
     location: {
         // Latitude and longitude for sun/moon calculations
         // Default: Passau, Germany