perf(Markdown): 题面、教程、AI 提示每次打开都去 unpkg.com 拉四个库，机房网络下又慢又不稳

md-editor-v3 的 MdPreview 不管正文里有没有代码、公式，都会从 unpkg.com 加载
highlight.js、katex、mermaid、echarts（mermaid 还是另一份 11.x）。而我们只用到最基础的
Markdown：题面 95% 是富文本存的 HTML，教程是标题、表格、图片，AI 输出是标题、列表、
表格、少量代码块，库里一处公式、mermaid 都没有。

- 显示：新组件 shared/components/Markdown.vue，直接用 markdown-it，代码高亮走本地的
  highlight.js（和练一练共用 shared/highlight.ts，补了 C++ / SQL）。9 处 MdPreview 全换掉。
  正文默认 16px，教程也统一成 16px。
- 编辑：后台教程编辑器换成项目已有的 CodeMirror，加一排格式按钮；图片可以按按钮选、
  粘贴、拖进来，都是先上传再插入。md-editor-v3 从依赖里删掉。
- AI 生成的内容（AI 提示、AI 分析、班级报告）不再放行原生 HTML：学生能在代码里诱导
  AI 吐出 <img onerror>，老师在后台一打开就执行。库里 1196 条 AI 输出没有一个 HTML
  标签，关掉不影响显示。题面、教程照旧放行。
- 长英文改成在单词之间折行，原来 break-all 会把 "I live" 断成 "I l / ive"。

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

apps/web/src/oj/problem/components/ProblemContent.vue

@@ -6,9 +6,7 @@ import { useProblemStore } from "oj/store/problem"
 import { DIFFICULTY } from "utils/constants"
 import { copyToClipboard, getTagColor } from "utils/functions"
 import { useSubmissionStore } from "oj/store/submission"
-import { useDark } from "@vueuse/core"
-import { MdPreview } from "md-editor-v3"
-import "md-editor-v3/lib/preview.css"
+import Markdown from "shared/components/Markdown.vue"
 import SqlProblemData from "./SqlProblemData.vue"
 import SimilarProblems from "./SimilarProblems.vue"
 import { isFlowchartPass, useFlowchartStore } from "oj/store/flowchart"
@@ -19,7 +17,6 @@ import { useProblemPageContext } from "../composables/problemPageContext"
 const ProblemFlowchart = defineAsyncComponent(() => import("./ProblemFlowchart.vue"))
 const MyFlowchart = defineAsyncComponent(() => import("./MyFlowchart.vue"))
 
-const isDark = useDark()
 const theme = useThemeVars()
 const problemStore = useProblemStore()
 const { problem } = storeToRefs(problemStore)
@@ -234,30 +231,18 @@ const astRequirements = computed(() => Object.entries(problem.value?.astRequirem
 
     <section class="block">
       <h3 class="title">描述</h3>
-      <MdPreview
-        preview-theme="vuepress"
-        :model-value="problem.description"
-        :theme="isDark ? 'dark' : 'light'"
-      />
+      <Markdown html :content="problem.description" />
     </section>
 
     <!-- 输入、输出一般都只有一两句，左右摆开省半屏 -->
     <div v-if="!isSQL" class="io">
       <section class="block">
         <h3 class="title">输入</h3>
-        <MdPreview
-          preview-theme="vuepress"
-          :model-value="problem.inputDescription"
-          :theme="isDark ? 'dark' : 'light'"
-        />
+        <Markdown html :content="problem.inputDescription" />
       </section>
       <section class="block">
         <h3 class="title">输出</h3>
-        <MdPreview
-          preview-theme="vuepress"
-          :model-value="problem.outputDescription"
-          :theme="isDark ? 'dark' : 'light'"
-        />
+        <Markdown html :content="problem.outputDescription" />
       </section>
     </div>
 
@@ -388,20 +373,12 @@ const astRequirements = computed(() => Object.entries(problem.value?.astRequirem
 
     <section v-if="problem.hint" class="block">
       <h3 class="title">提示</h3>
-      <MdPreview
-        preview-theme="preview"
-        :model-value="problem.hint"
-        :theme="isDark ? 'dark' : 'light'"
-      />
+      <Markdown html :content="problem.hint" />
     </section>
 
     <section v-if="problem.source" class="block">
       <h3 class="title">来源</h3>
-      <MdPreview
-        preview-theme="vuepress"
-        :model-value="problem.source"
-        :theme="isDark ? 'dark' : 'light'"
-      />
+      <Markdown html :content="problem.source" />
     </section>
 
     <SimilarProblems v-if="showSimilar" title="相似题目推荐" />
@@ -477,23 +454,6 @@ const astRequirements = computed(() => Object.entries(problem.value?.astRequirem
   border-left: 3px solid v-bind("theme.primaryColor");
 }
 
-/* md-editor 的预览自带一圈 padding、白底和段落外边距，放在小节标题下面显得很散 */
-:deep(.md-editor) {
-  background: transparent;
-}
-
-:deep(.md-editor-preview-wrapper) {
-  padding: 0;
-}
-
-:deep(.md-editor-preview > :first-child) {
-  margin-top: 0;
-}
-
-:deep(.md-editor-preview > :last-child) {
-  margin-bottom: 0;
-}
-
 .io {
   display: grid;
   grid-template-columns: repeat(2, minmax(0, 1fr));

apps/web/src/oj/problem/components/SubmissionResult.vue

@@ -23,9 +23,7 @@ import ResultHeader from "./ResultHeader.vue"
 import SimilarProblems from "./SimilarProblems.vue"
 import { useLessonStore } from "oj/store/lesson"
 import { useProblemPageContext } from "../composables/problemPageContext"
-import { MdPreview } from "md-editor-v3"
-import "md-editor-v3/lib/preview.css"
-import { useDark } from "@vueuse/core"
+import Markdown from "shared/components/Markdown.vue"
 
 const props = defineProps<{
   submission?: Submission
@@ -36,7 +34,6 @@ const props = defineProps<{
   peer?: boolean
 }>()
 
-const isDark = useDark()
 const problemStore = useProblemStore()
 const theme = useThemeVars()
 
@@ -390,12 +387,7 @@ const columns: DataTableColumn<JudgeCaseResult>[] = [
     <template v-if="showAIHint && hintTarget">
       <n-card size="small" class="hint-card">
         <n-spin v-if="hintLoading && !hintContent" size="small" />
-        <MdPreview
-          v-if="hintContent"
-          :model-value="hintContent"
-          preview-theme="vuepress"
-          :theme="isDark ? 'dark' : 'light'"
-        />
+        <Markdown v-if="hintContent" :content="hintContent" />
         <!-- 等级和「再多一点提示」。按钮出不出由后端 done 里的 canEscalate 定，
              前端不自己推阶梯（要再交一次才升得动，规则在 services/hint-level.ts） -->
         <n-flex