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/test_world/rooms/mod.rs

@@ -0,0 +1,9 @@
+//! Gauntlet room builders.
+//!
+//! Each room module exports a `spawn_entities()` function that creates
+//! entities in canonical order for deterministic StableId assignment.
+
+pub mod hub;
+pub mod inventory_warehouse;
+pub mod occlusion_corridor;
+pub mod pause_chamber;