fix(simulation): address PR #42 review — 8 items from Hoshe and Tyre

1. Sound producers: document empty v0.1 pipeline explicitly (critical)
2. Routine tests: add ActiveSim to 3 tests that passed trivially
3. Rename _observer_pos → observer_pos (used at line 191)
4. Add FactionOnly positive test case (matching faction_id)
5. Fix stale doc comment "Current: 9" → 10 in ObserverSnapshot
6. Remove orphaned SimulationTier/LastInteraction/ScopeTag types
7. Add tracing::warn on FactionOnly non-numeric parse failure
8. Document Medium-range occlusion gap as TODO in audible_at
9. Insert SoundEventQueue in observer test setup_world

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

server/src/bridge/types.rs

@@ -31,7 +31,7 @@ pub const PROTOCOL_VERSION: u8 = 10;
 /// v10 adds: sound_events (#124, D-038 server sound event pipeline).
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct ObserverSnapshot {
-    /// Protocol version for forward compatibility. Current: 9.
+    /// Protocol version for forward compatibility. Current: 10.
     pub version: u8,
     /// Simulation tick when this snapshot was produced
     pub tick: u64,