Rename screw tubes to screw conveyors (t44)

Player text says Screw conveyor; code uses screw (BP_SCREW, piece id
screw, screwIntake...). No compatibility code for old saves or
blueprints. Suite outputs match before and after apart from names.

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

src/sim/save.js

@@ -3,7 +3,7 @@
 const SAVE_VERSION = 2;
 const TOFF = 64; // temperatures are saved with an offset so sub-zero snow and ice survive
 function serializeWorld() {
-  // grains in flight from a tube or belt land where they are (rain in the air simply carries on)
+  // grains in flight from a screw or belt land where they are (rain in the air simply carries on)
   for (const f of flyers) if (!f.bag && !f.rain) landFlyer(f, Math.max(0, Math.min(W - 1, Math.floor(f.x))), Math.max(0, Math.min(H - 1, Math.floor(f.y))));
   flyers = flyers.filter(f => f.bag || f.rain);
   const t16 = new Uint16Array(N);
@@ -86,7 +86,7 @@ function deserializeWorld(meta, buffers) {
     const p = savedPart[i];
     if (p === P_WHEEL || p === P_INTAKE) continue;
     part[i] = p;
-    if (IS_TUBE[p]) markPow(i, true);
+    if (IS_SCREW[p]) markPow(i, true);
   }
   for (let i = 0; i < N; i++) { const m = mat[i]; if (m === BELTL || m === BELTR || m === SHAFT) markPow(i, true); }
   // Old machines removed from the game are refunded.