fix: LabelTemplate 序列化器允许 coder_ip 为空字符串/null

Why: DRF IPAddressField 默认拒绝空串, 前端清空 IP 保存时报 400

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/cm/serializers.py

@@ -43,6 +43,11 @@ class LabelMatSerializer(serializers.ModelSerializer):
     
 
 class LabelTemplateSerializer(CustomModelSerializer):
+    coder_ip = serializers.IPAddressField(required=False, allow_null=True, allow_blank=True)
+
     class Meta:
         model = LabelTemplate
         fields = '__all__'
+
+    def validate_coder_ip(self, value):
+        return value or None