Refactor CommandManager to manage command executor lifecycle and add shutdown method

core/src/main/java/com/xujiayao/discord_mc_chat/DMCC.java

@@ -152,6 +152,8 @@ public class DMCC {
 					serverInstance.shutdown();
 				}
 
+				CommandManager.shutdown();
+
 				// Do NOT clear event handlers here. They are registered once during mod initialization
 				// and should persist across DMCC reloads.
 				// EventManager.clear();

core/src/main/java/com/xujiayao/discord_mc_chat/commands/CommandManager.java

@@ -22,12 +22,16 @@ import java.util.concurrent.Executors;
 public class CommandManager {
 
 	private static final Map<String, Command> COMMANDS = new ConcurrentHashMap<>();
-	private static final ExecutorService COMMAND_EXECUTOR = Executors.newSingleThreadExecutor(ExecutorServiceUtils.newThreadFactory("DMCC-Command"));
+	private static ExecutorService commandExecutor;
 
 	/**
 	 * Initialize and register built-in commands based on the current operating mode.
 	 */
 	public static void initialize() {
+		if (commandExecutor == null || commandExecutor.isShutdown()) {
+			commandExecutor = Executors.newSingleThreadExecutor(ExecutorServiceUtils.newThreadFactory("DMCC-Command"));
+		}
+
 		COMMANDS.clear();
 
 		register(new HelpCommand());
@@ -38,6 +42,16 @@ public class CommandManager {
 		}
 	}
 
+	/**
+	 * Shutdown the command executor.
+	 */
+	public static void shutdown() {
+		if (commandExecutor != null) {
+			commandExecutor.shutdown();
+			commandExecutor = null;
+		}
+	}
+
 	/**
 	 * Register a command.
 	 *
@@ -63,7 +77,11 @@ public class CommandManager {
 	 * @param rawInput The raw command line
 	 */
 	public static void execute(CommandSender sender, String rawInput) {
-		COMMAND_EXECUTOR.submit(() -> {
+		if (commandExecutor == null || commandExecutor.isShutdown()) {
+			return;
+		}
+
+		commandExecutor.submit(() -> {
 			String line = rawInput == null ? "" : rawInput.trim();
 			if (line.isEmpty()) {
 				sender.reply(I18nManager.getDmccTranslation("terminal.unknown_command", rawInput));