loop: 用 rich.Markdown 渲染 assistant 输出

之前 console.print(f"...{content}") 只解析 [tag] 标签,不识别 **bold**、表格、列表
等 markdown 语法,LLM 回复会以原文显示。改成单独打印前缀后再 console.print(Markdown(content))。

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

core/loop.py

@@ -5,6 +5,7 @@ import json
 from typing import Any, Dict, Optional
 
 from rich.console import Console
+from rich.markdown import Markdown
 
 from .capabilities import ModelCapabilities
 from .llm import LLM
@@ -44,7 +45,8 @@ class AgentLoop:
             tool_calls = getattr(msg, "tool_calls", None) or []
             content = getattr(msg, "content", None)
             if content:
-                self.console.print(f"[cyan]assistant>[/cyan] {content}")
+                self.console.print("[cyan]assistant>[/cyan]")
+                self.console.print(Markdown(content))
 
             if not tool_calls:
                 return content or ""