refactor: cleanup unused imports, add conversation summary tracking

- Remove unused MarkdownRenderer import and field from ClaudeCodeComponent
- Add onFirstUserInput callback for conversation summary tracking
- Wire conversation summary in JinkReplSession

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

src/main/java/com/claudecode/tui/JinkReplSession.java

@@ -87,6 +87,11 @@ public class JinkReplSession {
         setupAgentCallbacks();
         setupToolContextCallbacks();
 
+        // 注册首次用户输入回调（用于对话摘要）
+        component.setOnFirstUserInput(text -> {
+            conversationSummary = text.length() > 40 ? text.substring(0, 40) : text;
+        });
+
         // 启动 jink 渲染
         inkApp = Ink.render(component);