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/html/posts/new.html

@@ -124,6 +124,27 @@
 
 {{template "layout/footer.html" .}}
 
-{{/* CodeMirror 6 (MIT License, via esm.sh bundle) */}}
+{{/* CodeMirror 6 importmap — 所有 @codemirror/@lezer 指向 esm.sh 同一构建树，共享依赖单例 */}}
+<script type="importmap">
+{
+    "imports": {
+        "@codemirror/state":          "https://esm.sh/@codemirror/state@6.5.2",
+        "@codemirror/view":           "https://esm.sh/@codemirror/view@6.36.4",
+        "@codemirror/commands":       "https://esm.sh/@codemirror/commands@6.8.1",
+        "@codemirror/language":       "https://esm.sh/@codemirror/language@6.11.0",
+        "@codemirror/lang-markdown":  "https://esm.sh/@codemirror/lang-markdown@6.3.2",
+        "@codemirror/language-data":  "https://esm.sh/@codemirror/language-data@6.5.1",
+        "@codemirror/autocomplete":   "https://esm.sh/@codemirror/autocomplete@6.18.6",
+        "@codemirror/search":         "https://esm.sh/@codemirror/search@6.5.10",
+        "@lezer/common":              "https://esm.sh/@lezer/common@1.2.3",
+        "@lezer/highlight":           "https://esm.sh/@lezer/highlight@1.2.1",
+        "@lezer/lr":                  "https://esm.sh/@lezer/lr@1.4.2",
+        "@lezer/markdown":            "https://esm.sh/@lezer/markdown@1.4.0",
+        "crelt":                      "https://esm.sh/crelt@1.0.6",
+        "style-mod":                  "https://esm.sh/style-mod@4.1.2",
+        "w3c-keyname":                "https://esm.sh/w3c-keyname@2.2.8"
+    }
+}
+</script>
 <script src="/static/js/common.js"></script>
 <script type="module" src="/static/js/editor.js"></script>