feat: 添加所有 Django apps 的 Serializers

- User Serializers（基础、详情、更新、统计）
- Region Serializers（基础、详情、树形结构）
- Moderation Serializers（版主申请、权限、支持、限制）
- Article Serializers（基础、创建、更新、审核、列表）
- FeaturedService Serializers（基础、创建、更新、审核、列表）
- Interaction Serializers（评论、评分、点赞、收藏）

backend/apps/users/serializers.py

@@ -3,12 +3,12 @@ from .models import User
 
 
 class UserSerializer(serializers.ModelSerializer):
-    """Serializer for User model."""
+    """Serializer for User model (basic info)."""
 
     class Meta:
         model = User
-        fields = ('id', 'username', 'email', 'first_name', 'last_name', 'avatar')
-        read_only_fields = ('id',)
+        fields = ('id', 'username', 'email', 'first_name', 'last_name', 'avatar', 'role', 'status')
+        read_only_fields = ('id', 'role', 'status')
 
 
 class UserDetailSerializer(serializers.ModelSerializer):
@@ -17,4 +17,22 @@ class UserDetailSerializer(serializers.ModelSerializer):
     class Meta:
         model = User
         fields = '__all__'
-        read_only_fields = ('id', 'date_joined', 'last_login')
+        read_only_fields = ('id', 'date_joined', 'last_login')
+
+
+class UserUpdateSerializer(serializers.ModelSerializer):
+    """Serializer for updating user profile."""
+
+    class Meta:
+        model = User
+        fields = ('first_name', 'last_name', 'avatar')
+
+
+class UserStatsSerializer(serializers.Serializer):
+    """Serializer for user statistics."""
+    articles_count = serializers.IntegerField()
+    services_count = serializers.IntegerField()
+    comments_count = serializers.IntegerField()
+    likes_count = serializers.IntegerField()
+    favorites_count = serializers.IntegerField()
+    ratings_count = serializers.IntegerField()