fix: interview create returns HTTP 201, frontend only accepted 200

NestJS POST 默认返回 201 Created，前端 startInterview() 和
sendAnswer() 只判断 statusCode === 200 导致成功创建也落入
else 分支显示创建面试失败。改为 >= 200 && < 300。

zhiyin-app/src/pages/interview/interview.vue

@@ -224,7 +224,7 @@ const startInterview = async () => {
       header: { 'Authorization': `Bearer ${token()}`, 'Content-Type': 'application/json' },
       data: { position: position.value },
     })
-    if (res.statusCode === 200 && res.data) {
+    if (res.statusCode >= 200 && res.statusCode < 300 && res.data) {
       interviewId.value = res.data.id
       messages.value = res.data.messages || messages.value
       answeredCount.value = res.data.questionCount || 0
@@ -274,7 +274,7 @@ const sendAnswer = async () => {
       header: { 'Authorization': `Bearer ${token()}`, 'Content-Type': 'application/json' },
       data: avatarMode.value ? { answer, avatar: true } : { answer },
     })
-    if (res.statusCode === 200 && res.data?.messages) {
+    if (res.statusCode >= 200 && res.statusCode < 300 && res.data?.messages) {
       const aiMsg = res.data.messages.find(m => m.role === 'ai')
       // Only push AI messages from response to avoid duplicating the user message already added above
       const newAiMessages = res.data.messages.filter(m => m.role === 'ai')