BGM does not play on linux if name is not all lower case

> Just noticed primal-beat-of-horrow_T.ogg doesn't play on Linux. Renaming it to primal-beat-of-horrow_t.ogg (with a lowercase 't') causes it to play correctly

> Probably because the game is looking for 'primal-beat-of-horrow_t.ogg' and can't find it because Linux file names are case sensitive

This may be related to the BGM switching I implemented which doesn't handle different file case when looking for files (although I thought such a thing would already be handled in the engine, but I might be bypassing it)

查看BGM切換的實作以及遊戲引擎如何處理檔案查找。該問題提到了Linux上的大小寫敏感問題，因此請檢查檔案路徑比較邏輯。首先找到BGM檔案被載入或引用的位置，很可能在音訊相關程式碼中。透過驗證修復是否允許在Linux上正確播放混合大小寫的檔案名稱來進行測試。

由索引模型根據 Issue 內容生成。