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-C3c正式互加好友实测-2026-09-30.json

@@ -0,0 +1,32 @@
+{
+  "time": "2026-09-30T15:35:10.2759067+08:00",
+  "api": "http://s101.local:18080/",
+  "accounts": [
+    "101",
+    "102"
+  ],
+  "authorization": "User explicitly allowed mutual friendship; 103-110 authorized if needed, unused",
+  "requests": [
+    {
+      "account": "101",
+      "route": "account/Login",
+      "mutation": false,
+      "http": 200,
+      "code": null,
+      "error": null
+    },
+    {
+      "account": "101",
+      "route": "playerdata/Get",
+      "mutation": false,
+      "http": 200,
+      "code": null,
+      "error": null
+    }
+  ],
+  "kvInputs": [],
+  "before": {},
+  "after": {},
+  "error": "MissingActualKVLevel",
+  "mutual": false
+}