Soften night sky: 55% bright (was 85%), wider star band

- skyDarkness 0.85 -> 0.55 so night sky is deep but not pitch
  black, leaving room for stars to show through
- skyMask widened (-0.10 -> -0.20 lower bound, 0.30 -> 0.40 upper)
  so stars appear closer to the horizon in the cockpit view
- Star tint multiplier 0.9 -> 1.0 (full bright) for clearer dots

vendor/clouds3d.js

@@ -148,10 +148,11 @@ var FRAG_SRC = [
         // 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);',
+        // Widened sky band so stars appear close to the horizon too.
+        'float skyMask = smoothstep(-0.20, 0.40, 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);',
+        'col = mix(col, uLight, clamp(stars, 0.0, 1.0));',
         // Density threshold: weather 'sunny' -> high (sparse clouds),
         // 'stormy' -> low (overcast deck).
         'float baseThresh = mix(0.72, 0.40, uDensity);',
@@ -189,7 +190,9 @@ var FRAG_SRC = [
         // them goes dark. transmittance tells us how much light made it
         // through the cloud layer (1 = clear, 0 = fully cloudy).
         'float cloud = 1.0 - trans;',
-        'float skyDarkness = nightFactor * 0.85;',
+        // 0.55 — strong but not pitch black, leaves room for stars to
+        // remain visible against a deep but not void-black sky.
+        'float skyDarkness = nightFactor * 0.55;',
         'col = mix(col, col * (1.0 - skyDarkness), 1.0 - cloud);',
         'gl_FragColor = vec4(col, 1.0);',
     '}'