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);
     }

topics/index.json

@@ -11,7 +11,7 @@
           "slug": "gc-jvm",
           "name": "GC / JVM / 三色标记",
           "description": "JVM 堆内存模型、GC 算法、三色标记法、垃圾收集器",
-          "path": "topics/gc-jvm",
+          "path": "topics/qunar-ai-fullstack/gc-jvm",
           "stats": {
             "total": 20,
             "by_type": {
@@ -24,7 +24,7 @@
           "slug": "ai-structured-output",
           "name": "AI 结构化输出 / Agent 架构",
           "description": "结构化输出方法、Agent 模式、受限解码",
-          "path": "topics/ai-structured-output",
+          "path": "topics/qunar-ai-fullstack/ai-structured-output",
           "stats": {
             "total": 20,
             "by_type": {
@@ -37,7 +37,7 @@
           "slug": "ai-memory",
           "name": "Agent 记忆管理 / 冲突处理",
           "description": "记忆分层架构、淘汰策略、冲突检测与消解",
-          "path": "topics/ai-memory",
+          "path": "topics/qunar-ai-fullstack/ai-memory",
           "stats": {
             "total": 20,
             "by_type": {
@@ -50,7 +50,7 @@
           "slug": "ai-hallucination",
           "name": "AI 幻觉 / 目标评价 / 规范",
           "description": "幻觉分类、Critic 架构、Context Engineering、评估体系",
-          "path": "topics/ai-hallucination",
+          "path": "topics/qunar-ai-fullstack/ai-hallucination",
           "stats": {
             "total": 20,
             "by_type": {
@@ -63,7 +63,7 @@
           "slug": "ai-tooling",
           "name": "AI 工具 / Harness / 综合",
           "description": "AI 工具选型、Harness 架构、可靠性保障、提效分析",
-          "path": "topics/ai-tooling",
+          "path": "topics/qunar-ai-fullstack/ai-tooling",
           "stats": {
             "total": 20,
             "by_type": {