fix(simulation): address PR #10 review — plugin wiring, stale reset, warnings

- Register KnowledgePlugin in main.rs and game_loop test (Tyre critical)
- Add KnowledgeGraph component to player spawn (Tyre critical)
- Reset Stale -> Active on fresh direct observation (Hoshe warning)
- Make registry/queue non-optional in emit_observation_events (Tyre/Hoshe)
- Add tracing::warn for missing EntityRegistry entries (Hoshe warning)
- Replace HashSet with Vec for small entity ID lookups (Hoshe suggestion)
- Add const static assertion for KnowledgeConfidence ordering (Hoshe)
- Add is_empty() and known_facts_iter() to KnowledgeGraph (Tyre)
- Add decay_skips_non_minute_ticks and observe_resets_stale tests (Hoshe)

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

server/tests/game_loop.rs

@@ -6,6 +6,7 @@ use settled_reach_server::bridge::framing::{read_framed, write_framed};
 use settled_reach_server::bridge::tcp::TcpBridge;
 use settled_reach_server::bridge::types::*;
 use settled_reach_server::bridge::{BridgePlugin, BridgeResource};
+use settled_reach_server::knowledge::{KnowledgeGraph, KnowledgePlugin};
 use settled_reach_server::simulation::movement::{PlayerCharacter, TilePosition, WalkabilityMap};
 use settled_reach_server::simulation::SimulationPlugin;
 use std::io::{BufReader, BufWriter};
@@ -26,10 +27,14 @@ fn player_moves_north_through_full_pipeline() {
         let mut app = App::new();
         app.add_plugins(SimulationPlugin);
         app.add_plugins(BridgePlugin);
+        app.add_plugins(KnowledgePlugin);
         app.insert_resource(BridgeResource::new(bridge));
         app.insert_resource(WalkabilityMap::new(32, 32, 1));
-        app.world_mut()
-            .spawn((PlayerCharacter, TilePosition::new(16, 16, 0)));
+        app.world_mut().spawn((
+            PlayerCharacter,
+            TilePosition::new(16, 16, 0),
+            KnowledgeGraph::new(),
+        ));
 
         // Run one tick: receive input, process, validate movement, generate snapshot, send
         app.update();