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-C2a自验汇总.json

@@ -0,0 +1,27 @@
+{
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+  "checkpointHashEntries": 33,
+  "originalReviewAndManifestUnchanged": true,
+  "outsideCodeWhitelist": [],
+  "diffCheck": 0,
+  "unityEditor": {
+    "success": true,
+    "errors": 0,
+    "warnings": 272
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+  "serviceHost": {
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+    "nonAndroidAssertions": 215,
+    "androidAggGroups": 16,
+    "androidAggAssertions": 215,
+    "formalRequests": 0
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+  "gameLoad": {
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+    "assertions": 2008,
+    "failed": 0,
+    "run": "20260929124717_40cff5b97587446bb1c9dd1b6ad5c2b1"
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+  "productionCallRuntimeVerified": false,
+  "playOrPackaging": false
+}