Force-run with Steam, but only in Steam versions

Currently, the Higurashi mod does not force the Steam version of the game to run through Steam, effectively breaking integration with Steam if the game is not ran from inside the Steam UI. We have a way in the installer to check whether the game is the Steam version or not. This code should be either ported to C# and added as a conditional check to the Steam API calls, or the installer should assist the game with Steam detection (e.g. by creating a file that informs the game whether or not this is the Steam version of the game).

該 issue 提到安裝程式有偵測 Steam 版本的方法；請找到該偵測程式碼。然後，將其移植到 C# 中以有條件地啟用 Steam API 呼叫，或修改安裝程式以建立一個標記檔案。檢查 C# 程式碼庫中現有的 Steam API 整合，以查看應在何處加入條件判斷。透過在 Steam UI 外部啟動遊戲來測試其 Steam 整合，以驗證修復。

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