Multi-core simulation: grain movement and heat across a worker pool (t88 phase 3)

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

src/manifest.json

@@ -37,6 +37,7 @@
     "sim/bot.js",
     "sim/ledger.js",
     "sim/weather.js",
+    "sim/workers.js",
     "sim/tick.js",
     "sim/worldgen-helpers.js",
     "sim/worldgen.js",
@@ -66,6 +67,7 @@
     "render/overlays.js",
     "ui/audio.js",
     "ui/state.js",
+    "ui/threads.js",
     "ui/title.js",
     "ui/saves.js",
     "ui/claims.js",