refactor(编辑器): 去掉 vue-codemirror，代码编辑器、协作编辑器、教程编辑器改用自己的薄外壳

三个编辑器只用到它的 v-model、extensions、只读、缩进、占位文字、尺寸和 ready，
shared/components/CodeMirror.vue 照它的做法写了这几样，功能和手感不变：
- 它默认带的 basicSetup（行号、撤销、折叠、搜索、括号……）照样带上
- 各项配置的先后顺序和它一致；外部改代码仍是一次不带 userEvent 的 changes，
  提交时的编辑过程统计不受影响
- @codemirror/commands 现在直接 import，显式声明进依赖

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

bun.lock

@@ -41,6 +41,7 @@
       "version": "1.9.0",
       "dependencies": {
         "@codemirror/autocomplete": "^6.20.3",
+        "@codemirror/commands": "^6.10.4",
         "@codemirror/lang-cpp": "^6.0.3",
         "@codemirror/lang-markdown": "^6.5.2",
         "@codemirror/lang-python": "^6.2.1",
@@ -76,7 +77,6 @@
         "pinyin-pro": "^3.29.5",
         "vue": "^3.5.43",
         "vue-chartjs": "^5.3.4",
-        "vue-codemirror": "^6.1.1",
         "vue-router": "^5.4.0",
         "y-codemirror.next": "^0.3.6",
         "y-protocols": "1.0.7",
@@ -1565,8 +1565,6 @@
 
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-    "vue-codemirror": ["vue-codemirror@6.1.1", "https://registry.npmjs.com/vue-codemirror/-/vue-codemirror-6.1.1.tgz", { "dependencies": { "@codemirror/commands": "6.x", "@codemirror/language": "6.x", "@codemirror/state": "6.x", "@codemirror/view": "6.x" }, "peerDependencies": { "codemirror": "6.x", "vue": "3.x" } }, "sha512-rTAYo44owd282yVxKtJtnOi7ERAcXTeviwoPXjIc6K/IQYUsoDkzPvw/JDFtSP6T7Cz/2g3EHaEyeyaQCKoDMg=="],
-
     "vue-demi": ["vue-demi@0.14.10", "https://registry.npmjs.com/vue-demi/-/vue-demi-0.14.10.tgz", { "peerDependencies": { "@vue/composition-api": "^1.0.0-rc.1", "vue": "^3.0.0-0 || ^2.6.0" }, "optionalPeers": ["@vue/composition-api"], "bin": { "vue-demi-fix": "bin/vue-demi-fix.js", "vue-demi-switch": "bin/vue-demi-switch.js" } }, "sha512-nMZBOwuzabUO0nLgIcc6rycZEebF6eeUfaiQx9+WSk8e29IbLvPU9feI6tqW4kTo3hvoYAJkMh8n8D0fuISphg=="],
 
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