feat(ai_chat): 添加Markdown渲染和图片生成功能

支持将AI回复的Markdown内容转换为HTML并渲染为美观的图片格式返回，提升聊天体验
```

```msg
feat(knowledge_base): 扩展知识库支持个人和群聊独立记忆

- 新增个人知识库功能，支持独立记忆
- 添加清除个人/群聊记忆命令
- 优化知识搜索逻辑，优先搜索个人记忆
- 更新插件帮助信息

plugins/ai_chat.py

@@ -4,9 +4,12 @@ AI 聊天插件，支持向量数据库记忆功能
 """
 import time
 import uuid
+import markdown
 from core.managers.command_manager import matcher
 from models.events.message import GroupMessageEvent, PrivateMessageEvent
+from models.message import MessageSegment
 from core.managers.vectordb_manager import vectordb_manager
+from core.managers.image_manager import image_manager
 from core.utils.logger import ModuleLogger
 from core.config_loader import global_config
 
@@ -113,7 +116,38 @@ async def chat_command(event: GroupMessageEvent | PrivateMessageEvent, args: lis
     user_message = " ".join(args)
     user_id = event.user_id
     group_id = getattr(event, 'group_id', 0)
+    user_name = event.sender.nickname or event.sender.card or str(user_id)
     
     await event.reply("正在思考中...")
     reply = await get_ai_response(user_id, group_id, user_message)
-    await event.reply(reply)
+    
+    # 将 Markdown 转换为 HTML
+    try:
+        # 启用扩展以支持代码块、表格等
+        html_reply = markdown.markdown(reply, extensions=['fenced_code', 'tables', 'nl2br'])
+    except Exception as e:
+        logger.error(f"Markdown 转换失败: {e}")
+        html_reply = reply.replace('\n', '<br>')
+    
+    # 渲染图片
+    try:
+        template_data = {
+            "user_name": user_name,
+            "user_message": user_message,
+            "ai_reply": html_reply
+        }
+        
+        base64_img = await image_manager.render_template_to_base64(
+            template_name="ai_chat.html",
+            data=template_data,
+            output_name=f"chat_{user_id}_{int(time.time())}.png",
+            image_type="png"
+        )
+        
+        if base64_img:
+            await event.reply(MessageSegment.image(f"base64://{base64_img}"))
+        else:
+            await event.reply("图片生成失败，返回文本：\n" + reply)
+    except Exception as e:
+        logger.error(f"渲染聊天图片失败: {e}")
+        await event.reply("图片生成失败，返回文本：\n" + reply)