test(simulation): map-agnostic invariant tests, 36 invariants (#508)

Adds test_world::invariants with 29 world-query invariants (structural,
perception, population, simulation) and 7 system-execution tests. All
invariants are gated behind the gauntlet feature and run against the
fully-initialized gauntlet world. Documents StableId ranges through
Sprint 14 rooms.

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

server/src/test_world/mod.rs

@@ -38,6 +38,8 @@
 
 #[cfg(feature = "gauntlet")]
 pub mod constants;
+#[cfg(feature = "gauntlet")]
+pub mod invariants;
 pub mod reset;
 #[cfg(feature = "gauntlet")]
 pub mod rooms;
@@ -536,6 +538,9 @@ mod tests {
 
         setup_gauntlet(&mut app);
 
+        // Run all 29 world-query invariants against the fully-initialized gauntlet world.
+        invariants::run_invariants(app.world_mut());
+
         let registry = app.world().resource::<EntityRegistry>();
         assert_eq!(
             registry.len(),