Buildings cast no shadows: daylight passes player-built pieces (t37)

The lighting finds its own roof per column, skipping walls, belts, tubes, machines and molds,
and lets light through them like air, in both looks. Natural rock still shades; the
simulation's roof (steam condensing under a built roof) is unchanged. New test/t_light.js.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/render/world.js

@@ -219,7 +219,7 @@ function drawWorld() {
           else cl = 5;
         }
         top = cl << 24;
-        fpx[row + bx] = (tb ? 0xff000000 : 0) | (cl === 5 ? 0xff0000 : 0) | (cl === 3 ? 0xff00 : 0) | (cl === 1 || cl === 4 || cl === 6 ? 0xff : 0);
+        fpx[row + bx] = (tb ? 0xff000000 : 0) | (cl === 5 ? 0xff0000 : 0) | (cl === 3 ? 0xff00 : 0) | (cl === 1 && !builtForLight(i, x, y) ? 0xff : 0);
       }
       if (fv < 255) {
         const k = fv / 255; r *= k; g *= k; b *= k;