fix(simulation): address PR #12 review — z-level filter, visible tile dedup, version bump

- Filter remembered entities by z-level (Hoshe + Tyre warning)
- Skip remembered ghosts on currently visible tiles (Hoshe warning)
- Bump ObserverSnapshot version to 3 (Tyre suggestion)
- Add edge case tests: visible tile collision, different z-level,
  knowledge without position (Hoshe suggestion)
- Regenerate msgpack fixtures for v3

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

server/src/bridge/mod.rs

@@ -107,7 +107,7 @@ pub fn generate_snapshot(
         visible.len()
     );
     buffer.snapshot = Some(ObserverSnapshot {
-        version: 2,
+        version: 3,
         tick: time.tick,
         game_time,
         player_facing: FacingDirection::default(),

server/src/bridge/types.rs

@@ -12,11 +12,12 @@ pub use crate::simulation::time::DayPhase;
 /// Contains all information visible to the observer at a given tick.
 ///
 /// v2 adds: game_time, player_facing, visible_tiles, visibility sectors.
+/// v3 adds: relationship (D-033 entity color), observation (Visible/Remembered).
 /// Future fields: ambient sound events, internal monologue triggers,
 /// HUD state (D-020 expansion).
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct ObserverSnapshot {
-    /// Protocol version for forward compatibility. Current: 2.
+    /// Protocol version for forward compatibility. Current: 3.
     pub version: u8,
     /// Simulation tick when this snapshot was produced
     pub tick: u64,