fix: 修复前端访问错误

docker-compose.yml

@@ -22,6 +22,18 @@ services:
       context: ./backend
     container_name: exam-helper-backend
     restart: unless-stopped
+    healthcheck:
+      test:
+        [
+          "CMD",
+          "python",
+          "-c",
+          "import urllib.request; urllib.request.urlopen('http://127.0.0.1:8000/health', timeout=3).read()",
+        ]
+      interval: 5s
+      timeout: 5s
+      retries: 12
+      start_period: 25s
     # AI 相关变量优先从 .env.example 注入；若存在 .env 则覆盖同名项（见 Compose env_file 顺序）
     env_file:
       - .env.example
@@ -46,7 +58,8 @@ services:
     container_name: exam-helper-frontend
     restart: unless-stopped
     depends_on:
-      - backend
+      backend:
+        condition: service_healthy
     ports:
       - "127.0.0.1:8173:80"