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/bridge/mod.rs

@@ -0,0 +1,40 @@
+// Bridge module - Client-server communication
+// Implements D-020 subprocess/IPC architecture
+// MessagePack serialization for Rust<->Godot communication
+
+use bevy_app::prelude::*;
+
+pub mod types;
+pub use types::*;
+
+/// Error type for bridge operations
+#[derive(Debug, thiserror::Error)]
+pub enum BridgeError {
+    #[error("serialization error: {0}")]
+    Serialization(#[from] rmp_serde::encode::Error),
+    #[error("deserialization error: {0}")]
+    Deserialization(#[from] rmp_serde::decode::Error),
+    #[error("transport error: {0}")]
+    Transport(String),
+}
+
+/// Abstracts transport layer (D-020)
+/// Implemented by LocalBridge (stdio) and future NetworkBridge
+pub trait SimBridge: Send + Sync {
+    /// Send an observer snapshot to the client
+    fn send_snapshot(&self, snapshot: &ObserverSnapshot) -> Result<(), BridgeError>;
+
+    /// Receive player inputs from the client
+    fn receive_inputs(&self) -> Result<Vec<PlayerInput>, BridgeError>;
+}
+
+/// Bridge plugin for client-server communication
+/// Abstracts transport layer (LocalBridge/NetworkBridge)
+pub struct BridgePlugin;
+
+impl Plugin for BridgePlugin {
+    fn build(&self, _app: &mut App) {
+        // Stub implementation - will be populated in phase 2
+        tracing::debug!("BridgePlugin initialized");
+    }
+}