feat(simulation): sprint 12 server — tier system, sound events, KG access, line previewer

Implements 4 completed tickets + partial progress on 2 more:

- #93 Tier marker components (ActiveSim, BackgroundSim, StateSaved + TierPlugin)
- #138 Information tag schema (ObserverAccess enum in knowledge/types.rs)
- #124 Sound event system (SoundEventEmitter, SoundEventQueue, bridge wiring)
- #193 Line previewer CLI (line_preview binary with filter/explain/sequence modes)
- #94 Active tier simulation (in progress — With<ActiveSim> filters)
- #139 Component-level access control (in progress — filter_by_access)

Updates snapshot fixtures and test golden files for new sound_events field.

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

server/src/simulation/path_follow.rs

@@ -8,6 +8,7 @@ use bevy_ecs::prelude::*;
 use crate::npc::Npc;
 use crate::simulation::movement::MoveIntent;
 use crate::simulation::pathfinding::{ComputedPath, PathBlocked};
+use crate::simulation::tier::ActiveSim;
 
 /// Movement speed component. Controls ticks between path steps.
 /// Default: 1 step per tick. Higher values = slower movement.
@@ -48,9 +49,13 @@ impl MovementSpeed {
 
 /// System: NPC entities with ComputedPath advance along their path.
 /// Creates MoveIntent for the next step. Removes ComputedPath when complete.
+///
+/// Scoped to `ActiveSim` NPCs — only entities in the Active tier execute
+/// path movement each tick (D-026, #94). Background/StateSaved NPCs do not
+/// process path steps.
 pub fn follow_paths(
     mut commands: Commands,
-    mut query: Query<(Entity, &mut ComputedPath, Option<&mut MovementSpeed>), With<Npc>>,
+    mut query: Query<(Entity, &mut ComputedPath, Option<&mut MovementSpeed>), (With<Npc>, With<ActiveSim>)>,
 ) {
     for (entity, mut path, speed_opt) in query.iter_mut() {
         if let Some(mut speed) = speed_opt {