Add spawn/delete commands, fix session state and entity broadcast

- marathonctl now supports spawn/delete entity commands
- Fixed session state bug (was transitioning to Left every 5s)
- Fixed entity broadcast to detect Added<NetworkedEntity>
- Added AppCommandQueue pattern for app-level control commands

References: #131, #132

crates/app/src/main.rs

@@ -205,6 +205,7 @@ fn main() {
     // Insert control socket path as resource
     app.insert_resource(control::ControlSocketPath(args.control_socket.clone()));
     app.add_systems(Startup, control::start_control_socket_system);
+    app.add_systems(Update, (control::process_app_commands, control::cleanup_control_socket));
 
     // Rendering-only plugins
     #[cfg(not(feature = "headless"))]