feat(simulation): sprint 9 gauntlet — test infrastructure and first 3 rooms

Add Gauntlet test world with 3 rooms (Inventory Warehouse, Occlusion
Corridor, Pause Chamber) + Central Hub, room constants module, room
reset trigger mechanism, Layer 3 subprocess integration test, golden
file comparison engine and test suite, and content runtime validation.

Tickets: #482, #484, #485, #487, #488, #489, #490

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/main.rs

@@ -114,8 +114,12 @@ fn main() {
     // Override SimRng with the chosen seed (SimulationPlugin defaults to seed 0)
     app.insert_resource(settled_reach_server::simulation::rng::SimRng::new(seed));
 
-    // Gauntlet content loader is future scope — proof room for all modes.
-    setup_proof_room(&mut app);
+    // Gauntlet test world for --test-mode, proof room for normal mode.
+    if test_mode {
+        settled_reach_server::test_world::setup_gauntlet(&mut app);
+    } else {
+        setup_proof_room(&mut app);
+    }
 
     tracing::info!(
         "Simulation initialized (seed={}, test_mode={})",