feat: 多用户系统改造（数据模型 + 认证 API）

backend/authentication/serializers.py

@@ -0,0 +1,34 @@
+from rest_framework import serializers
+from django.contrib.auth.models import User
+from django.contrib.auth import authenticate
+
+class UserSerializer(serializers.ModelSerializer):
+    class Meta:
+        model = User
+        fields = ['id', 'username', 'email', 'date_joined']
+        read_only_fields = ['date_joined']
+
+class RegisterSerializer(serializers.ModelSerializer):
+    password = serializers.CharField(write_only=True, min_length=6)
+    
+    class Meta:
+        model = User
+        fields = ['username', 'email', 'password']
+    
+    def create(self, validated_data):
+        user = User.objects.create_user(
+            username=validated_data['username'],
+            email=validated_data.get('email', ''),
+            password=validated_data['password']
+        )
+        return user
+
+class LoginSerializer(serializers.Serializer):
+    username = serializers.CharField()
+    password = serializers.CharField(write_only=True)
+    
+    def validate(self, data):
+        user = authenticate(**data)
+        if user and user.is_active:
+            return user
+        raise serializers.ValidationError("用户名或密码错误")