Fix night sky: visible clouds, real moon-driven darkening

Three coordinated changes:
1. nightPaletteNew.cloud: void -> raised (slightly lighter than
   sky) so clouds have contrast against the new-moon sky
2. nightPaletteFull.cloudShadow: panel -> void so cloud undersides
   fade into the night sky, while the lit topsides (border) stand
   out clearly
3. getNightColor() now keeps 'light' (moonlight) bright and only
   partially darkens sky/bg. The previous version squashed
   everything toward black, killing cloud structure.

Shader side:
- max(0.15, uDayProgress) keeps a baseline moonlight tint on the
  lit side of clouds even when uDayProgress happens to be 0
- The final darken pass is now driven by nightFactor (sunAlt-based)
  instead of the unreliable uDayProgress

vendor/clouds3d.js

@@ -141,12 +141,13 @@ var FRAG_SRC = [
         'float skyT = clamp(rd.y * 0.7 + 0.5, 0.0, 1.0);',
         'vec3 col = mix(uBg, uSky, skyT);',
         // Stars: hash-grid sphere, above horizon, only at night.
-        // Night = sun altitude below 0. Visibility extends well into the
-// lower half of the sky so the airplane-cockpit view shows stars
-// from the horizon up.
+// Night = sun altitude below 0. Visibility extends well into the
+        // lower half of the sky so the airplane-cockpit view shows stars
+        // from the horizon up.
         'float nightFactor = smoothstep(0.05, -0.15, uSunAlt);',
         'float skyMask = smoothstep(-0.10, 0.30, rd.y);',
         'float stars = starField(rd) * skyMask * nightFactor;',
+        // (nightFactor is also used below for the final darken pass.)',
         'col = mix(col, uLight, clamp(stars, 0.0, 1.0) * 0.9);',
         // Density threshold: weather 'sunny' -> high (sparse clouds),
         // 'stormy' -> low (overcast deck).
@@ -169,7 +170,7 @@ var FRAG_SRC = [
                 'float lit = clamp((p.y + 0.3) / 2.1, 0.0, 1.0);',
                 'vec3 cloudCol = mix(uCloudShadow, uCloud, lit);',
                 // Sun tint on the lit side, fades at night
-                'cloudCol = mix(cloudCol, uLight, uDayProgress * 0.35 * lit);',
+                'cloudCol = mix(cloudCol, uLight, max(0.15, uDayProgress) * 0.35 * lit);',
                 'float alpha = clamp(d * stepSize * 0.9, 0.0, 1.0);',
                 'col = mix(col, cloudCol, alpha * trans);',
                 'trans *= (1.0 - alpha);',
@@ -177,8 +178,10 @@ var FRAG_SRC = [
             '}',
             't += stepSize;',
         '}',
-        // Night darkening
-        'col = mix(col, mix(uBg, col, 0.4), (1.0 - uDayProgress) * 0.55);',
+        // Night darkening — driven by sun altitude, not uDayProgress
+        // (uDayProgress is the 0..1 clock progress through 24h, which
+        // is not the same as 'is it night').
+        'col = mix(col, mix(uBg, col, 0.4), nightFactor * 0.45);',
         'gl_FragColor = vec4(col, 1.0);',
     '}'
 ].join('\n');