Uphill runs share one cleat phase; no cleats downhill; pick slope bands

A piece added to a running sloped belt kept its own cleat phase, so at
the seam a rib could start just behind another and push its pocket into
it, stalling the whole run with only a few grains. Every block of a run
now takes the phase of the run's lower-left block.

Downhill sloped belts no longer have cleats: they carry like a flat belt
(90 grains/s, was 38) and draw only the sidewall.

Middle click on a sloped belt's band, where it is drawn into the empty
block beside it, now picks the belt.

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

src/sim/conveyors.js

@@ -106,7 +106,8 @@ function carryBeltsAndFilters(belts, filters, d, bm, carrying) {
     if (above === BELTL || above === BELTR || netSat(b) <= 0) continue;
     if (carrying) {
       if (PH[above] === PH_LIQUID) beltDrain(b);
-      if (!isSlopeBelt(code)) carryColumn(b - W, d, null); // on a slope, the cleats do the carrying
+      // uphill, the cleats do the carrying
+      if (!isSlopeBelt(code) || !slopeUphill(code, (y >> 2) * BW + (x >> 2))) carryColumn(b - W, d, null);
     }
   }
 }