[Steam Deck][Proton] Saves do not persist on Steam Deck running through Proton

Had a user report that on Steam Deck with Proton 9.0-4, their saves didn't persist.

> Had a question, I installed 07th mod on Umineko on steam deck and everything works fine, except that the saves I make while playing on deck disappear when I close and open the game again

This may be a side effect of our system which disables steam cloud, and writes saves to the `mysav` folder.

For the time being I've told them to try running the native version to see if it fixes it.

If anyone has a similar problem see this wiki article for how to change from Proton to Native (Steam Linux Runtime) https://wiki.07th-mod.com/Umineko/Umineko-Part-3a-Cross-Platform-Installer/#steam-instructions-for-enablingdisabling-proton_1

該 issue 提到存檔被寫入 'mysav' 資料夾，並且某個系統禁用了 Steam Cloud。首先定位存檔檔案處理程式碼，很可能在與遊戲資料持久化相關的 C# 腳本中。檢查在 Proton 與原生 Linux 上如何確定存檔路徑。透過在 Steam Deck 或 Proton 環境中測試來驗證行為，並查看 'mysav' 資料夾路徑是否正確解析，或者權限是否存在問題。

由索引模型根據 Issue 內容生成。