fix(simulation): address PR #39 review — 3 warnings + 6 suggestions

Warnings fixed:
- contraband.rs: scan event now always emits even when NPC already
  knows (was skipped by early `continue`). Contract matches doc.
- test_world/mod.rs: ScanEventBuffer added to player spawn bundle
  so check_contraband_scan doesn't silently no-op in gauntlet mode.
- npc/mod.rs → simulation/mod.rs: moved check_contraband_scan
  registration to SimulationPlugin (operates on player inventory and
  snapshot pipeline, consistent with process_talk_interaction).

Suggestions addressed:
- cross_room_transitions.rs T1: clarified standalone position vs
  constants.rs observer position in comment.
- dialogue.rs: Vec<&str> dedup replaced with BTreeSet<&str> for
  deterministic iteration (project convention).
- contraband.rs: added test for multiple simultaneous ScanAuthority
  NPCs in range (564 tests total).
- dialogue.rs: doc-comment on relationship_to_trust explaining
  KnowledgeConfidence ordering and Suspects default.
- cross_room_transitions.rs T5: noted direct KG API usage vs full
  perception system.
- sprint_gauntlet.rs: documented intentional Contentment { level: 0 }.
- content_scaling.rs: noted GAUNTLET_NPC_COUNT is manually maintained.
- contraband.rs: doc-comment on cross-plugin registration rationale.

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

server/src/simulation/mod.rs

@@ -39,6 +39,9 @@ impl Plugin for SimulationPlugin {
                     movement::validate_movement.after(path_follow::follow_paths),
                     path_follow::cleanup_path_blocked.after(movement::validate_movement),
                     listening::update_listening_focus.after(movement::validate_movement),
+                    contraband::check_contraband_scan
+                        .after(movement::validate_movement)
+                        .before(crate::perception::observer::compute_observer_snapshot),
                     time::advance_tick.after(path_follow::cleanup_path_blocked),
                 ),
             );