Downhill sloped belts draw as plain belts, ghosts and previews too

Downhill runs have no cleats, so they no longer draw the sidewall or
ribs either: placed, as ghosts, or in the drag preview, which now knows
the belt's direction. Uphill runs keep the wall and ribs.

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

src/sim/conveyors.js

@@ -107,7 +107,7 @@ function carryBeltsAndFilters(belts, filters, d, bm, carrying) {
     if (carrying) {
       if (PH[above] === PH_LIQUID) beltDrain(b);
       // uphill, the cleats do the carrying
-      if (!isSlopeBelt(code) || !slopeUphill(code, (y >> 2) * BW + (x >> 2))) carryColumn(b - W, d, null);
+      if (!isSlopeBelt(code) || !slopeUphill(code, blockV[(y >> 2) * BW + (x >> 2)])) carryColumn(b - W, d, null);
     }
   }
 }