feat(server): initialize Rust/bevy_ecs simulation server

Server boilerplate epic (276) complete. Establishes the Rust simulation
server foundation per D-020 (subprocess/IPC architecture).

Structure:
- bevy_ecs 0.18 + bevy_app 0.18, MessagePack serialization (rmp-serde)
- SimulationPlugin with deterministic resources: SimulationTime (D-031),
  SimRng (D-030), InputQueue (D-010)
- Core IPC types: ObserverSnapshot, PlayerInput, SimBridge trait (D-020)
- CauseChain production component for provenance tracking (D-030)
- SimulationTier types with LRU eviction support (D-026)
- NPC 10-axis model components (D-024)
- 15 tests: inline unit tests + integration smoke/serialization tests
- make ci-server passes (clippy, fmt, build, test)

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

server/src/simulation/tier.rs

@@ -0,0 +1,58 @@
+// Simulation tier system
+// Implements D-026: Active/Background/State-saved/Ungenerated tiers
+// Timestamp-based LRU eviction for simulation space management
+
+use bevy_ecs::prelude::*;
+use serde::{Deserialize, Serialize};
+
+#[derive(Component, Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
+pub enum SimulationTier {
+    Active,
+    Background,
+    StateSaved,
+    Ungenerated,
+}
+
+#[derive(Component, Debug, Clone)]
+pub struct LastInteraction {
+    pub tick: u64,
+}
+
+#[derive(Component, Debug, Clone)]
+pub struct ScopeTag {
+    pub tags: Vec<ScopeKind>,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Hash, Serialize, Deserialize)]
+pub enum ScopeKind {
+    Neighborhood,
+    ActiveQuest,
+    Colleague,
+    KnownContact,
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn tier_can_be_added_and_queried() {
+        let mut world = bevy_ecs::world::World::new();
+        let entity = world.spawn(SimulationTier::Active).id();
+        assert_eq!(
+            *world.get::<SimulationTier>(entity).unwrap(),
+            SimulationTier::Active
+        );
+    }
+
+    #[test]
+    fn tier_can_transition() {
+        let mut world = bevy_ecs::world::World::new();
+        let entity = world.spawn(SimulationTier::Active).id();
+        world.entity_mut(entity).insert(SimulationTier::Background);
+        assert_eq!(
+            *world.get::<SimulationTier>(entity).unwrap(),
+            SimulationTier::Background
+        );
+    }
+}