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/tests/serialization.rs

@@ -0,0 +1,51 @@
+//! IPC serialization round-trip tests (D-030 Layer 1: fixture-based).
+
+use settled_reach_server::bridge::types::*;
+
+#[test]
+fn observer_snapshot_roundtrip() {
+    let snapshot = ObserverSnapshot {
+        tick: 42,
+        entities: vec![VisibleEntity {
+            entity_id: 1,
+            x: 10.0,
+            y: 20.0,
+            z: 0,
+            kind: EntityKind::Npc,
+        }],
+    };
+
+    let bytes = rmp_serde::to_vec(&snapshot).expect("serialize");
+    let decoded: ObserverSnapshot = rmp_serde::from_slice(&bytes).expect("deserialize");
+
+    assert_eq!(decoded.tick, 42);
+    assert_eq!(decoded.entities.len(), 1);
+    assert_eq!(decoded.entities[0].entity_id, 1);
+}
+
+#[test]
+fn player_input_roundtrip() {
+    let input = PlayerInput {
+        tick: 100,
+        action: PlayerAction::MoveNorth,
+    };
+
+    let bytes = rmp_serde::to_vec(&input).expect("serialize");
+    let decoded: PlayerInput = rmp_serde::from_slice(&bytes).expect("deserialize");
+
+    assert_eq!(decoded.tick, 100);
+}
+
+#[test]
+fn empty_snapshot_roundtrip() {
+    let snapshot = ObserverSnapshot {
+        tick: 0,
+        entities: vec![],
+    };
+
+    let bytes = rmp_serde::to_vec(&snapshot).expect("serialize");
+    let decoded: ObserverSnapshot = rmp_serde::from_slice(&bytes).expect("deserialize");
+
+    assert_eq!(decoded.tick, 0);
+    assert!(decoded.entities.is_empty());
+}

server/tests/smoke.rs

@@ -0,0 +1,22 @@
+//! Smoke test: the simulation world boots and can run a single tick.
+
+use bevy_app::prelude::*;
+use settled_reach_server::simulation::SimulationPlugin;
+use settled_reach_server::simulation::time::SimulationTime;
+
+#[test]
+fn world_boots_and_ticks() {
+    let mut app = App::new();
+    app.add_plugins(SimulationPlugin);
+
+    // Verify initial state
+    let time = app.world().resource::<SimulationTime>();
+    assert_eq!(time.tick, 0);
+
+    // Run one update cycle
+    app.update();
+
+    // Verify tick advanced
+    let time = app.world().resource::<SimulationTime>();
+    assert_eq!(time.tick, 1);
+}