fix singbox endpoints proxy chain not work

v2rayN/ServiceLib/Models/SingboxConfig.cs

@@ -40,6 +40,7 @@ public class Route4Sbox
     public bool? auto_detect_interface { get; set; }
     public List<Rule4Sbox> rules { get; set; }
     public List<Ruleset4Sbox>? rule_set { get; set; }
+    public string? final { get; set; }
 }
 
 [Serializable]

v2rayN/ServiceLib/Services/CoreConfig/CoreConfigSingboxService.cs

@@ -1118,6 +1118,7 @@ public class CoreConfigSingboxService
     {
         try
         {
+            singboxConfig.route.final = Global.ProxyTag;
             singboxConfig.route.rules.Insert(0, new()
             {
                 outbound = Global.DirectTag,