feat(upserver): 保存M2客户端KV迁移至本人统计写检查点

保存独立KV用户服务、固定会话存档与原业务接线，以及C3d资料缓存和C3e本人统计写。
保留原PF/AGG路线、业务公式和时序；榜单读取、好友资料、公告、匹配及首场景闸仍待完成。

验证：ServiceHost两条件各33组646断言；Unity CLI Loop编译0错误269警告。
包含相关方案、评审裁决、测试及状态文档。未操作服务器、正式账号或打包。

CodexOutput/upserver/B3BatchMigration/M2/M2-合批-C2c-旧奖励首败日志.json

@@ -0,0 +1,15 @@
+{
+  "TotalCount": 1,
+  "DisplayedCount": 1,
+  "LogType": "Error",
+  "MaxCount": 12,
+  "SearchText": "NullReferenceException",
+  "IncludeStackTrace": true,
+  "Logs": [
+    {
+      "Type": "Error",
+      "Message": "NullReferenceException: Object reference not set to an instance of an object",
+      "StackTrace": "GameCore.GuideDataCenter.Init () (at Assets/Scripts/DataCenter/DataCenter.GuideData.cs:100)\nSystem.Runtime.CompilerServices.AsyncMethodBuilderCore+<>c.<ThrowAsync>b__7_0 (System.Object state) (at <1071a2cb0cb3433aae80a793c277a048>:0)\nUnityEngine.UnitySynchronizationContext+WorkRequest.Invoke () (at <b0b044832c86429e90c306261f4bbd83>:0)\nUnityEngine.UnitySynchronizationContext.Exec () (at <b0b044832c86429e90c306261f4bbd83>:0)\nUnityEngine.UnitySynchronizationContext.ExecuteTasks () (at <b0b044832c86429e90c306261f4bbd83>:0)"
+    }
+  ]
+}