fix(simulation): address PR #125 review — tick truncation, ordering, perf, protocol test

- Widen EventPort tick methods from u32 to u64 (prevents overflow)
- Add is_identity() guard on hot-path String allocation in modifiers
- Replace Vec::remove(0) with VecDeque::pop_front() in price history
- Add .after(tick_economy_simulation) ordering for debug commands
- Fix stale PROTOCOL_VERSION assertion (20 → 21) in serialization test
- Add D-181 Phase 2 visibility scope comment on serve_econ_state_query
- Eliminate double lookup in rebuild_signals via single-pass extraction
- Track economy seed TODO with backlog ticket reference

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/src/simulation/mod.rs

@@ -168,7 +168,7 @@ impl Plugin for SimulationPlugin {
         app.init_resource::<ticker::TickerPool>();
 
         // Economy simulation (#821, D-031) — loaded once at startup, no-op when DB absent.
-        // Uses seed 0 for now; will be threaded through StartupMessage world seed (#TODO).
+        // Uses seed 0 for now; will be threaded through StartupMessage world seed (#826).
         if let Some((econ_sim, econ_state)) = economy::try_load_economy(0) {
             app.insert_resource(econ_sim).insert_resource(econ_state);
         }