fix: add default md handler

apps/md.js

@@ -0,0 +1,23 @@
+import plugin from '../../../lib/plugins/plugin.js'
+import cfg from '../../../lib/config/config.js'
+export class ChatGPTMarkdownHandler extends plugin {
+  constructor () {
+    super({
+      name: 'chatgptmd处理器',
+      priority: -100,
+      namespace: 'chatgpt-plugin',
+      handler: [{
+        key: 'chatgpt.markdown.convert',
+        fn: 'mdHandler'
+      }]
+    })
+  }
+
+  async mdHandler (e, options, reject) {
+    if (cfg.bot.global_md) {
+      const { content, prompt, use } = options
+      let md = `> ${prompt}\n\n---\n${content}\n\n---\n*当前模式：${use}*`
+      return md
+    }
+  }
+}