fix(editor): 修复Tiptap编辑器mention和emoji的文本转换问题

修改tiptapToString函数以正确处理mention节点和emoji节点的文本转换
添加mention配置参数char、allowSpaces和allowedPrefixes

src/components/editor/TiptapEditor.vue

@@ -209,6 +209,9 @@ const editor = useEditor({
       },
       suggestion: {
         ...suggestion,
+        char: '@',           
+        allowSpaces: false,  
+        allowedPrefixes: null, 
         items: ({ query }) => {
           return suggestion.items({ 
             query, 
@@ -496,7 +499,36 @@ function tiptapToMessage() {
 function tiptapToString() {
   if (!editor.value) return ''
   
-  return editor.value.getText()
+  const json = editor.value.getJSON()
+  let result = ''
+  
+  const processInlines = nodes => {
+    nodes.forEach(node => {
+      if (node.type === 'text') {
+        result += node.text
+      } else if (node.type === 'mention') {
+        result += `@${node.attrs.label} `
+      } else if (node.type === 'emoji') {
+        // 关键修改：使用表情的alt文本而不是忽略
+        result += node.attrs.alt || ''
+      } else if (node.type === 'hardBreak') {
+        result += '\n'
+      }
+    })
+  }
+  
+  if (json.content) {
+    json.content.forEach(node => {
+      if (node.type === 'paragraph') {
+        if (node.content) {
+          processInlines(node.content)
+        }
+        result += '\n'
+      }
+    })
+  }
+  
+  return result.trim()
 }