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/utils/types.ts

@@ -128,6 +128,7 @@ export interface Problem {
   share_submission: boolean
   contest: number
   my_status: number
+  my_failed_count?: number
   visible: boolean
 
   // 流程图相关字段