feat(simulation): contraband detection + dialogue confidence gate (D-075) (#425, #524)

Contraband detection (Task #425, D-065):
- New module: simulation/contraband.rs — NPC scan checks carried items
  against the KnowledgeGraph confidence gate. NPCs with Authority access
  can initiate a scan; scan outcome depends on item CarriedBy + KG entry.
- Adds ContrabandScanResult event type and ContrabanEntry component.
- Wired into simulation/mod.rs module list.

Dialogue confidence gate (Task #524, D-075 — OQ-18 resolution):
- relationship_to_trust() gains confidence parameter (KnowledgeConfidence).
- Trust tier mapping: (Friendly, KnowsDetails+)→Secret, (Friendly|Known,
  KnowsOf+)→Real, otherwise Surface. Access tier (Layer 1) unchanged.
- Caller process_talk_interaction passes observer KG confidence_of target.
- Resolves OQ-18: confidence co-gates TrustTier, not AccessTier.

Supporting changes:
- decisions/content.md: add D-075 (16 decisions, dated 2026-02-19)
- knowledge/types.rs: expose KnowledgeConfidence comparison helpers
- knowledge/registry.rs: minor API polish
- bridge/types.rs: ContrabandScanResult wire type
- bridge/text_renderer.rs: render contraband scan status
- perception/observer: include carried item count in snapshot
- npc/mod.rs: NPC scan range constant, authority flag

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

server/src/perception/observer/tests.rs

@@ -2106,10 +2106,7 @@ fn npc_behind_wall_appears_in_blocked_entities() {
         "NPC behind wall should appear in blocked_entities"
     );
     // Not in visible entities
-    let npc_visible = snapshot
-        .entities
-        .iter()
-        .any(|e| e.entity_id == npc_sid.0);
+    let npc_visible = snapshot.entities.iter().any(|e| e.entity_id == npc_sid.0);
     assert!(!npc_visible, "NPC should not be in visible entities");
 }