feat(simulation): multi-threaded executor + EntityRng (#843 Part B)

Enable Bevy multi-threaded executor via bevy_tasks multi_threaded
feature. Systems within the same TickPhase that don't share mutable
resources now run in parallel automatically.

Add EntityRng component — per-entity ChaCha20Rng seeded from
world_seed + StableId via splitmix64 mixing. More deterministic than
shared SimRng (order-independent). Migrate all monologue systems
(4 of 13 SimRng consumers) to EntityRng, removing contention that
serialized them against conversation/dialogue systems.

Add rayon dependency (infrastructure only, no par_iter calls yet).

SimRng retained for world-level randomness: conversation pairing,
knowledge transfer, dialogue, ticker, storyteller.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/src/main.rs

@@ -199,7 +199,7 @@ fn main() {
             std::process::exit(1);
         }
     } else {
-        setup_proof_room(&mut app, archetype);
+        setup_proof_room(&mut app, archetype, seed);
     }
 
     tracing::info!(
@@ -395,9 +395,11 @@ fn dump_schedule_graph() {
 fn setup_proof_room(
     app: &mut App,
     archetype: settled_reach_server::bridge::types::CharacterArchetype,
+    world_seed: u64,
 ) {
     use settled_reach_server::knowledge::registry::EntityRegistry;
     use settled_reach_server::knowledge::KnowledgeGraph;
+    use settled_reach_server::simulation::rng::EntityRng;
     use settled_reach_server::npc::relationships::{RelationshipEdge, RelationshipGraph};
     use settled_reach_server::npc::{
         Contentment, DailyRoutine, Npc, RelationshipKind, RoutineEntry, ToleranceThreshold, Want,
@@ -459,7 +461,10 @@ fn setup_proof_room(
             PlayerMoveCooldown::default(),
         ))
         .id();
-    registry.register(player);
+    let player_sid = registry.register(player);
+    app.world_mut()
+        .entity_mut(player)
+        .insert(EntityRng::from_seed_and_id(world_seed, player_sid.0));
 
     // NPC 1: Dock worker at (16,13) — behind wall, full routine
     let npc1 = app
@@ -507,6 +512,9 @@ fn setup_proof_room(
         ))
         .id();
     let npc1_sid = registry.register(npc1);
+    app.world_mut()
+        .entity_mut(npc1)
+        .insert(EntityRng::from_seed_and_id(world_seed, npc1_sid.0));
 
     // NPC 2: Field tech at (14,18) — visible to player, has routine
     let npc2 = app
@@ -544,6 +552,9 @@ fn setup_proof_room(
         ))
         .id();
     let npc2_sid = registry.register(npc2);
+    app.world_mut()
+        .entity_mut(npc2)
+        .insert(EntityRng::from_seed_and_id(world_seed, npc2_sid.0));
 
     // NPC 3: Guard at (18,14) — stationary, no routine
     let npc3 = app
@@ -565,6 +576,9 @@ fn setup_proof_room(
         ))
         .id();
     let npc3_sid = registry.register(npc3);
+    app.world_mut()
+        .entity_mut(npc3)
+        .insert(EntityRng::from_seed_and_id(world_seed, npc3_sid.0));
 
     // Populate RelationshipGraph with a few edges
     {