fix: 改用 importmap + esm.sh 解决 CodeMirror 多实例冲突

- 将 import 改回 bare specifier，通过 importmap 指向 esm.sh
- esm.sh 在同一构建上下文中能识别共享依赖，确保 @codemirror/state 单例
- 消除 "Unrecognized extension value" instanceof 检查错误

templates/MetaLab-2026/static/js/editor.js

@@ -1,28 +1,17 @@
 /**
  * MetaLab Markdown Editor — CodeMirror 6 版
  *
- * 功能：
- * - CodeMirror 6 编辑器，Markdown 语法高亮
- * - 工具栏：加粗/斜体/删除线/行内代码/标题/链接/图片/引用/代码块/列表/表格/分割线
- * - 快捷键：Ctrl+B/I/K/` Shift+I Tab Shift+Tab Ctrl+S Ctrl+Shift+P F11
- * - 粘贴图片 / 拖拽上传 / 进度反馈
- * - 分屏实时预览（Ctrl+Shift+P 切换）
- * - 代码块语言下拉选择器
- * - 自动保存草稿（localStorage + 后端）
- * - 字数/行数/阅读时间统计
- * - 全屏编辑模式（F11）
- * - 滚动同步（分屏模式下）
- *
- * CodeMirror 6 通过 esm.sh bundle 加载，所有依赖自动解析。
+ * 依赖通过 importmap 指向 esm.sh，所有 @codemirror/@lezer 共享同一构建树，
+ * 避免多实例导致的 "Unrecognized extension value" 错误。
  */
-import { EditorState } from 'https://esm.sh/@codemirror/state@6.5.2';
-import { EditorView, keymap, lineNumbers, highlightActiveLine, drawSelection } from 'https://esm.sh/@codemirror/view@6.36.4';
-import { defaultKeymap, history, historyKeymap, indentWithTab } from 'https://esm.sh/@codemirror/commands@6.8.1';
-import { markdown, markdownLanguage } from 'https://esm.sh/@codemirror/lang-markdown@6.3.2';
-import { languages } from 'https://esm.sh/@codemirror/language-data@6.5.1';
-import { syntaxHighlighting, defaultHighlightStyle } from 'https://esm.sh/@codemirror/language@6.11.0';
-import { searchKeymap } from 'https://esm.sh/@codemirror/search@6.5.10';
-import { autocompletion } from 'https://esm.sh/@codemirror/autocomplete@6.18.6';
+import { EditorState } from '@codemirror/state';
+import { EditorView, keymap, lineNumbers, highlightActiveLine, drawSelection } from '@codemirror/view';
+import { defaultKeymap, history, historyKeymap, indentWithTab } from '@codemirror/commands';
+import { markdown, markdownLanguage } from '@codemirror/lang-markdown';
+import { languages } from '@codemirror/language-data';
+import { syntaxHighlighting, defaultHighlightStyle } from '@codemirror/language';
+import { searchKeymap } from '@codemirror/search';
+import { autocompletion } from '@codemirror/autocomplete';
 
 /* ================================================================
    DOM 引用