feat: 数学闯关前端页面

重写self-quiz.vue为纯数学闯关页面（3步流程：设定挑战→出题答题→过关统计），api.js新增getMathQuizStart/verifyMathAnswer/completeMathQuiz接口。

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

cfc-frontend/utils/api.js

@@ -1459,3 +1459,16 @@ export const getLeaderboardTop = () => {
 export const getLeaderboardMyRank = () => {
   return request('/api/leaderboard/my-rank', 'POST')
 }
+
+// ===== 数学闯关（自己出题自己答） =====
+export const getMathQuizStart = (childId, age) => {
+  return request('/api/wisdom/math/start', 'POST', { childId, age })
+}
+
+export const verifyMathAnswer = (childId, expression, userAnswer) => {
+  return request('/api/wisdom/math/verify', 'POST', { childId, expression, userAnswer })
+}
+
+export const completeMathQuiz = (data) => {
+  return request('/api/wisdom/math/complete', 'POST', data)
+}