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>

tools/scenes/t35-diagonal.js

@@ -0,0 +1,7 @@
+// Run after clear-sky.js: a belt takes sand from a pile, up a diagonal screw to an upper belt.
+const tx = BX + 12, ty = BY - 1;
+for (let x = BX + 3; x < tx; x++) placeBlock(BP_BELT, 1, x, BY, true);
+for (let k = 0; k < 10; k++) placeBlock(BP_TUBE, 4, tx + k, ty - k, true);
+for (let x = tx + 10; x < tx + 18; x++) placeBlock(BP_BELT, 1, x, ty - 9, true);
+for (let y = BY * 4 - 22; y < BY * 4; y++) for (let x = (BX + 4) * 4; x < (BX + 11) * 4; x++) setCell(y * W + x, SAND, 20, 0);
+window.CAM = [(tx + 4) * 4, (ty - 4) * 4];