Diagonal screw tubes, laid by a 45° drag (t35)

- Tubes run in eight directions: a drag at about 45° lays a diagonal run, R cycles all eight.
- Diagonal runs carry grains at the straight rate (120 grains/s), join straight tubes and belts,
  keep grains in at the corners, pass water, and carry bars level.
- New part ids 11-14 (saved ids are never renumbered); tube checks use an IS_TUBE table.
- New test/t_diag_tubes.js (85 checks).

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

src/sim/save.js

@@ -86,7 +86,7 @@ function deserializeWorld(meta, buffers) {
     const p = savedPart[i];
     if (p === P_WHEEL || p === P_INTAKE) continue;
     part[i] = p;
-    if (p >= P_TU && p <= P_TR) markPow(i, true);
+    if (IS_TUBE[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.