Push ground horizon lower in frame

gmask smoothstep end -0.10 -> -0.30: ground only fully fills when
ray Y is below -0.30 (about 17° below horizon). The horizon line
sits higher in the frame, more sky visible above.

vendor/clouds3d.js

@@ -203,7 +203,7 @@ var FRAG_SRC = [
         'float fogAmount = clamp(tGround / 30.0, 0.0, 1.0);',
         'groundCol = mix(groundCol, uBg, fogAmount * 0.75);',
         // Ground mask: full ground when looking down, none when up.
-        'float gmask = (tGround > 0.0) ? smoothstep(0.0, -0.10, rd.y) : 0.0;',
+        'float gmask = (tGround > 0.0) ? smoothstep(0.0, -0.30, rd.y) : 0.0;',
         'col = mix(col, groundCol, gmask);',
         'gl_FragColor = vec4(col, 1.0);',
     '}'