feat: 首页配置封面图上传预览，修复系列活动跳转，活动卡片样式优化

backend/competition/views.py

@@ -14,14 +14,24 @@ from .serializers import (
 from rest_framework.pagination import PageNumberPagination
 
 
-@api_view(['GET'])
+@api_view(['GET', 'PATCH'])
 @permission_classes([permissions.AllowAny])
 def get_homepage_config(request):
-    """获取首页配置"""
+    """获取或更新首页配置（PATCH 支持 multipart/form-data 上传图片）"""
     try:
         config = HomePageConfig.objects.filter(is_active=True).first()
         if not config:
             config = HomePageConfig.objects.create()
+
+        if request.method == 'PATCH':
+            serializer = HomePageConfigSerializer(
+                config, data=request.data, partial=True, context={'request': request}
+            )
+            if serializer.is_valid():
+                serializer.save()
+                return Response(serializer.data)
+            return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)
+
         serializer = HomePageConfigSerializer(config, context={'request': request})
         return Response(serializer.data)
     except Exception as e: