feat(编辑器): 添加清除事件常量并优化提及功能

在事件总线常量中添加 editor:clear 事件类型
优化提及功能，确保编辑器获得焦点后光标位置正确

src/components/editor/CustomEditor.vue

@@ -783,6 +783,20 @@ const onSubscribeMention = (data) => {
   // 确保编辑器获得焦点
   editorRef.value?.focus()
   
+  // 如果编辑器为空或者光标不在编辑器内，将光标移动到编辑器末尾
+  const selection = window.getSelection()
+  if (!selection.rangeCount || !editorRef.value.contains(selection.anchorNode)) {
+    const range = document.createRange()
+    if (editorRef.value.lastChild) {
+      range.setStartAfter(editorRef.value.lastChild)
+    } else {
+      range.setStart(editorRef.value, 0)
+    }
+    range.collapse(true)
+    selection.removeAllRanges()
+    selection.addRange(range)
+  }
+  
   // 插入@提及
   insertMention(data)
 }

src/constant/event-bus.ts

@@ -5,5 +5,6 @@ export const enum ContactConst {
 export const enum EditorConst {
   Mention = 'editor:mention',
   Quote = 'editor:quote',
-  Edit = 'editor:edit'
+  Edit = 'editor:edit',
+  Clear = 'editor:clear'
 }