fix: convert question_files from dict to list in all interview-prep meta.json

topics/interview-prep/ai-engineering/meta.json

@@ -3,13 +3,13 @@
   "name": "AI工程实践",
   "description": "Context Engineer、Harness Engineer、智能体架构、MCP协议、权限治理、可插拔配置",
   "tags": [],
-  "question_files": {
-    "single_choice": "single_choice.json",
-    "true_false": "true_false.json",
-    "fill_blank": "fill_blank.json",
-    "short_answer": "short_answer.json",
-    "code_reading": "code_reading.json"
-  },
+  "question_files": [
+    "single_choice",
+    "true_false",
+    "fill_blank",
+    "short_answer",
+    "code_reading"
+  ],
   "stats": {
     "total": 35,
     "by_type": {

topics/interview-prep/database-advanced/meta.json

@@ -3,13 +3,13 @@
   "name": "数据库进阶",
   "description": "B+树索引优化、EXPLAIN执行计划、Redis集群/哨兵、混合持久化、慢查询优化",
   "tags": [],
-  "question_files": {
-    "single_choice": "single_choice.json",
-    "true_false": "true_false.json",
-    "fill_blank": "fill_blank.json",
-    "short_answer": "short_answer.json",
-    "code_reading": "code_reading.json"
-  },
+  "question_files": [
+    "single_choice",
+    "true_false",
+    "fill_blank",
+    "short_answer",
+    "code_reading"
+  ],
   "stats": {
     "total": 35,
     "by_type": {

topics/interview-prep/distributed-microservice/meta.json

@@ -3,13 +3,13 @@
   "name": "分布式微服务架构",
   "description": "服务注册与发现、负载均衡、限流熔断、配置中心、幂等控制、分布式锁、分布式事务",
   "tags": [],
-  "question_files": {
-    "single_choice": "single_choice.json",
-    "true_false": "true_false.json",
-    "fill_blank": "fill_blank.json",
-    "short_answer": "short_answer.json",
-    "code_reading": "code_reading.json"
-  },
+  "question_files": [
+    "single_choice",
+    "true_false",
+    "fill_blank",
+    "short_answer",
+    "code_reading"
+  ],
   "stats": {
     "total": 45,
     "by_type": {

topics/interview-prep/go-java-concurrency/meta.json

@@ -3,13 +3,13 @@
   "name": "Go/Java并发模型",
   "description": "GMP调度、CSP模型、AQS/ForkJoinPool、goroutine泄漏、JMM、happens-before、pprof/JFR",
   "tags": [],
-  "question_files": {
-    "single_choice": "single_choice.json",
-    "true_false": "true_false.json",
-    "fill_blank": "fill_blank.json",
-    "short_answer": "short_answer.json",
-    "code_reading": "code_reading.json"
-  },
+  "question_files": [
+    "single_choice",
+    "true_false",
+    "fill_blank",
+    "short_answer",
+    "code_reading"
+  ],
   "stats": {
     "total": 45,
     "by_type": {

topics/interview-prep/k8s-observability/meta.json

@@ -3,13 +3,13 @@
   "name": "K8s与可观测性",
   "description": "K8s应用发布、弹性扩缩容、灰度发布、健康检查、可观测体系建设",
   "tags": [],
-  "question_files": {
-    "single_choice": "single_choice.json",
-    "true_false": "true_false.json",
-    "fill_blank": "fill_blank.json",
-    "short_answer": "short_answer.json",
-    "code_reading": "code_reading.json"
-  },
+  "question_files": [
+    "single_choice",
+    "true_false",
+    "fill_blank",
+    "short_answer",
+    "code_reading"
+  ],
   "stats": {
     "total": 45,
     "by_type": {

topics/interview-prep/message-queue/meta.json

@@ -3,13 +3,13 @@
   "name": "消息队列",
   "description": "主流中间件选型、路由、持久化原理、事务、死信队列、推拉模式、集群化部署",
   "tags": [],
-  "question_files": {
-    "single_choice": "single_choice.json",
-    "true_false": "true_false.json",
-    "fill_blank": "fill_blank.json",
-    "short_answer": "short_answer.json",
-    "code_reading": "code_reading.json"
-  },
+  "question_files": [
+    "single_choice",
+    "true_false",
+    "fill_blank",
+    "short_answer",
+    "code_reading"
+  ],
   "stats": {
     "total": 45,
     "by_type": {