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/npc/routine.rs

@@ -125,6 +125,7 @@ mod tests {
         let entity = world
             .spawn((
                 Npc,
+                ActiveSim,
                 TilePosition::new(5, 5, 0),
                 DailyRoutine {
                     entries: vec![RoutineEntry {
@@ -153,6 +154,7 @@ mod tests {
         let entity = world
             .spawn((
                 Npc,
+                ActiveSim,
                 loc, // Already at afternoon location
                 DailyRoutine {
                     entries: vec![RoutineEntry {
@@ -181,6 +183,7 @@ mod tests {
         let entity = world
             .spawn((
                 Npc,
+                ActiveSim,
                 TilePosition::new(5, 5, 0),
                 DailyRoutine {
                     entries: vec![RoutineEntry {