perf: reduce cloud march steps

vendor/clouds3d.js

@@ -720,7 +720,7 @@ var FRAG_SRC = [
             'float maxMarch = max(1.0, uCloudMaxMarch);',
             'tExit = min(tExit, tEnter + maxMarch);',
             'if (tExit <= tEnter) { gl_FragColor = vec4(0.0); return; }',
-            'float stepSize = (tExit - tEnter) / 48.0;',
+            'float stepSize = (tExit - tEnter) / 32.0;',
             'float t = tEnter + stepSize * 0.5;',
             'float coverage = clamp(uDensity, 0.0, 1.0);',
             'float baseThresh = mix(0.62, 0.20, coverage);',
@@ -730,7 +730,7 @@ var FRAG_SRC = [
             'float phase = 0.30 + 0.70 * pow(max(0.0, cosT), 2.5);',
             'float trans = 1.0;',
             'vec3 cloudSum = vec3(0.0);',
-            'for (int i = 0; i < 24; i++) {',
+            'for (int i = 0; i < 32; i++) {',
                 'vec3 p = uCamPos + rd * t;',
                 'p += rd * (ign(gl_FragCoord.xy + vec2(float(i) * 7.13, float(i) * 3.71)) - 0.5) * stepSize * 0.25;',
                 'float alt = p.y + earthDrop(p.xz);',