feat(engine): add rng_seed to ObserverSnapshot for deterministic replay (#527)

Add rng_seed: Option<u64> to ObserverSnapshot (protocol v10). Populated
from SimRng state each tick. Completes the WRONG button capture loop —
seed.txt now writes a valid u64 instead of "unavailable", enabling
deterministic replay from bug reports.

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

server/src/perception/observer/mod.rs

@@ -21,6 +21,7 @@ use crate::simulation::interaction::NearbyInteractionBuffer;
 use crate::simulation::inventory::{CarriedBy, InventorySlot, ItemName};
 use crate::simulation::monologue::{MonologueBuffer, SprintAnomalyQueue};
 use crate::simulation::movement::{PlayerCharacter, TilePosition, WalkabilityMap};
+use crate::simulation::rng::SimRng;
 use crate::simulation::stance::Stance;
 use crate::simulation::time::SimulationTime;
 
@@ -81,6 +82,7 @@ pub fn compute_observer_snapshot(
     )>,
     inventory_items: Query<(Entity, &CarriedBy, &ItemName, &InventorySlot)>,
     mut buffer: ResMut<SnapshotBuffer>,
+    sim_rng: Option<Res<SimRng>>,
 ) {
     let Ok((
         observer_entity,
@@ -215,6 +217,7 @@ pub fn compute_observer_snapshot(
         dialogue_response,
         blocked_entities,
         scan_events,
+        rng_seed: sim_rng.as_deref().map(|r| r.seed()),
     });
 }