Throughput in the info overlay: grains per second and backing-up glow (t49)

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

src/sim/tick.js

@@ -14,6 +14,7 @@ function simTick() {
   if (tick % 8 === 0) wakeBotPowder();
   simMove();
   heatPass();
+  if (flowOn) flowTick();
   for (let c = 0; c < NCH; c++) if (awake[c]) awake[c]--;
   if (tick % 15 === 0) checkMolds();
   if (tick % 30 === 0) checkLedger();