feat(simulation): add input processing, snapshot gen, and game loop

Implements the full server-side tick pipeline:
- process_player_input drains InputQueue, converts PlayerActions to
  MoveIntent components or pause/unpause toggles
- generate_snapshot builds ObserverSnapshot from ECS state with
  render coordinate conversion
- receive_bridge_inputs/send_bridge_snapshot handle bridge I/O with
  graceful disconnect detection via ServerRunning resource
- main.rs now accepts TCP connections and runs a proper game loop
- PlayerCharacter marker, Player EntityKind, SnapshotBuffer resource

Closes server side of #81, #82, #83.

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

server/src/main.rs

@@ -4,7 +4,9 @@
 use bevy_app::prelude::*;
 use tracing_subscriber::{layer::SubscriberExt, util::SubscriberInitExt};
 
-use settled_reach_server::bridge::BridgePlugin;
+use settled_reach_server::bridge::tcp::TcpBridge;
+use settled_reach_server::bridge::{BridgePlugin, BridgeResource, ServerRunning};
+use settled_reach_server::simulation::movement::{PlayerCharacter, TilePosition, WalkabilityMap};
 use settled_reach_server::simulation::SimulationPlugin;
 
 fn main() {
@@ -17,15 +19,36 @@ fn main() {
         .with(tracing_subscriber::fmt::layer())
         .init();
 
+    let addr = std::env::args()
+        .nth(1)
+        .or_else(|| std::env::var("SR_ADDR").ok())
+        .unwrap_or_else(|| "127.0.0.1:9876".to_string());
+
     tracing::info!("The Settled Reach - Simulation Server starting");
+    tracing::info!("Waiting for client connection on {}", addr);
+
+    let bridge = TcpBridge::accept(&addr).expect("Failed to accept client connection");
+    tracing::info!("Client connected, initializing simulation");
 
     // Create the bevy App and add plugins
     let mut app = App::new();
     app.add_plugins(SimulationPlugin);
     app.add_plugins(BridgePlugin);
+    app.insert_resource(BridgeResource::new(bridge));
+    app.insert_resource(WalkabilityMap::new(32, 32, 1));
+    app.world_mut()
+        .spawn((PlayerCharacter, TilePosition::new(16, 16, 0)));
 
-    // Single tick for smoke verification; real game loop in phase 2
-    app.update();
+    tracing::info!("Simulation initialized, entering game loop");
 
-    tracing::info!("Simulation server update complete");
+    // Game loop: run until client disconnects
+    loop {
+        app.update();
+        // Check ServerRunning resource
+        if !app.world().resource::<ServerRunning>().0 {
+            break;
+        }
+    }
+
+    tracing::info!("Simulation server shutting down");
 }