fix: clip cloud rays at terrain distance

vendor/clouds3d.js

@@ -703,6 +703,7 @@ var FRAG_SRC = [
                     'vec3 pT = uCamPos + rd * dist;',
                     'float terrainAlt = (pT.y + earthDrop(pT.xz)) / max(1.0, uTerrainExag);',
                     'if (terrainAlt > uCloudTop + 0.05) { gl_FragColor = vec4(0.0); return; }',
+                    'tExit = min(tExit, dist - 0.02);',
                 '}',
             '}',
             'tExit = min(tExit, tEnter + 30.0);',