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>

docs/systems/stone-and-liquids.md

@@ -5,7 +5,7 @@ Built 2026-10-22; the uses for stone and sand were added 2026-10-23.
 - Code:
   - `src/sim/processors.js` (Refiner, Stone cutter, Silo);
   - `src/sim/pipes.js`;
-  - `src/sim/conveyors.js` and `src/sim/machine-tick.js` (belts and tubes);
+  - `src/sim/conveyors.js` and `src/sim/machine-tick.js` (belts and screw conveyors);
   - `src/sim/economy.js` (prices, builders' orders).
 - Tests: `test/t_pipes.js`, `test/t_stone.js`, `test/t_conveyors.js`.
 
@@ -57,12 +57,12 @@ through another refiner.
 - **Water accounting.** Water in pipes counts in the world's water total, so the weather never
   sends rain to replace it. Pipe contents are saved.
 
-## Belts and screw tubes
+## Belts and screw conveyors
 - A heap on a belt moves as one: the whole stack, up to 96 grains deep, steps along together
   instead of only its bottom layer. The owner reports that big piles still only move at the top
   (see NOTES.md).
-- Screw tubes run at belt pace, moving every other tick.
-  - A horizontal tube fed from a full hopper moves about 100–110 grains a second.
+- Screw conveyors run at belt pace, moving every other tick.
+  - A horizontal screw conveyor fed from a full hopper moves about 100–110 grains a second.
   - A belt under its mouth keeps up, carrying a stream 3–5 grains deep at about the same rate.
   - A vertical lift brings up about 40–60 grains a second.
   - `tools/experiments/flow.js` measures these.