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/oj/api.ts

@@ -301,6 +301,12 @@ export function getAILoginSummary() {
   return http.get("ai/login_summary")
 }
 
+// ==================== 相似题目推荐 ====================
+
+export function getSimilarProblems(problemId: string) {
+  return http.get("problem/similar", { params: { problem_id: problemId } })
+}
+
 // ==================== 流程图相关API ====================
 
 export function submitFlowchart(data: {