refactor: 目录结构增加 Topic 层级 topics/qunar-ai-fullstack/

子主题目录从 topics/{slug} 移至 topics/qunar-ai-fullstack/{slug}
前端 fetch 路径改用 subtopic.path 字段

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

index.html

@@ -345,13 +345,13 @@ async function selectTopic(slug) {
   if (!topic) return;
 
   try {
-    // Load meta to get question file list
-    const metaRes = await fetch(`topics/${slug}/meta.json`);
+    const topicPath = topic.path;
+    const metaRes = await fetch(`${topicPath}/meta.json`);
     const meta = await metaRes.json();
 
     currentQuestions = [];
     for (const typeFile of meta.question_files) {
-      const qRes = await fetch(`topics/${slug}/${typeFile}.json`);
+      const qRes = await fetch(`${topicPath}/${typeFile}.json`);
       const qData = await qRes.json();
       currentQuestions.push(...qData.questions);
     }