feat: add teaching enhancement features

1. AI personalized hints after 3 failures (streaming SSE)
2. Submission error distribution panel in "my submissions" tab
3. Similar problem recommendations on AC or 3+ failures
4. Admin stuck problems analysis page

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/admin/api.ts

@@ -434,3 +434,8 @@ export function getProblemSetProgress(problemSetId: number) {
 export function removeUserFromProblemSet(problemSetId: number, userId: number) {
   return http.delete(`admin/problemset/${problemSetId}/progress/${userId}`)
 }
+
+// 学生卡点分析
+export function getStuckProblems() {
+  return http.get("admin/problem/stuck")
+}

src/admin/problem/Stuck.vue

@@ -0,0 +1,56 @@
+<script setup lang="ts">
+import { getStuckProblems } from "admin/api"
+
+interface StuckProblem {
+  problem_id: string
+  problem_title: string
+  total: number
+  failed: number
+  failed_users: number
+  ac_rate: number
+}
+
+const loading = ref(true)
+const data = ref<StuckProblem[]>([])
+
+const columns: DataTableColumn<StuckProblem>[] = [
+  { title: "题目 ID", key: "problem_id", width: 100 },
+  { title: "题目名称", key: "problem_title", minWidth: 200 },
+  { title: "总提交", key: "total", width: 100, sorter: "default" },
+  { title: "失败次数", key: "failed", width: 100, sorter: "default" },
+  {
+    title: "卡住学生数",
+    key: "failed_users",
+    width: 120,
+    sorter: "default",
+    defaultSortOrder: "descend",
+  },
+  {
+    title: "AC 率",
+    key: "ac_rate",
+    width: 100,
+    sorter: "default",
+    render: (row) => `${row.ac_rate}%`,
+  },
+]
+
+onMounted(async () => {
+  try {
+    const res = await getStuckProblems()
+    data.value = res.data
+  } finally {
+    loading.value = false
+  }
+})
+</script>
+
+<template>
+  <h2 style="margin-top: 0">学生卡点分析</h2>
+  <n-data-table
+    :loading="loading"
+    :columns="columns"
+    :data="data"
+    striped
+    :pagination="{ pageSize: 20 }"
+  />
+</template>