fix: /help命令动态展示全部28个已注册命令

- CommandContext增加commandRegistry字段
- HelpCommand从registry动态获取命令列表（不再硬编码6个）
- 自动对齐命令名称，附显示别名

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/main/java/com/claudecode/repl/ReplSession.java

@@ -192,7 +192,7 @@ public class ReplSession {
                 statusLine.enable(providerInfo.model(), agentLoop.getTokenTracker());
             }
 
-            CommandContext cmdContext = new CommandContext(agentLoop, toolRegistry, out, () -> running = false);
+            CommandContext cmdContext = new CommandContext(agentLoop, toolRegistry, commandRegistry, out, () -> running = false);
 
             while (running) {
                 String input;
@@ -272,7 +272,7 @@ public class ReplSession {
 
         Scanner scanner = new Scanner(System.in);
         this.activeScanner = scanner;
-        CommandContext cmdContext = new CommandContext(agentLoop, toolRegistry, out, () -> running = false);
+        CommandContext cmdContext = new CommandContext(agentLoop, toolRegistry, commandRegistry, out, () -> running = false);
 
         while (running) {
             out.print(AnsiStyle.BOLD + AnsiStyle.BRIGHT_CYAN + "❯ " + AnsiStyle.RESET);