refactor(simulation): address PR #72 review suggestions

- Hoshe #3: replace O(n²) Vec scan in fallback NPC assignment with
  BTreeSet; prevent same NPC assigned to two roles in one triangle
- Hoshe #4: add From impls for RoleId, TriangleId, StableId, and
  TriangleCrisisEventWire — eliminate fragile .0 access on newtypes
- Hoshe #5: consolidate near-identical unit tests with integration
  counterparts — keep only unique tests in #[cfg(test)] module
- Tyre #3: replace O(N*M) scan in apply_resolve_triangle with
  BTreeMap<TriangleId, Entity> index for O(1) per-command lookup
- Tyre #4: document &mut World on generate_intra_template_triangles
- Observer snapshot uses TriangleCrisisEventWire::from instead of
  manual field mapping

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

server/src/perception/observer/mod.rs

@@ -393,16 +393,7 @@ pub fn compute_observer_snapshot(
     let triangle_crisis_events = crisis_queue
         .drain()
         .into_iter()
-        .map(|e| TriangleCrisisEventWire {
-            triangle_id: e.triangle_id.0,
-            role_assignments: e
-                .role_assignments
-                .into_iter()
-                .map(|(role, sid)| (role.0, sid.0))
-                .collect(),
-            trigger_npc_id: e.trigger_npc.0,
-            tick: e.tick,
-        })
+        .map(TriangleCrisisEventWire::from)
         .collect();
 
     buffer.snapshot = Some(ObserverSnapshot {