[Enhancement] 永久保存自定义实例图标

[ToobLac]

Closes #5485

目前暂定保存在当前启动器实例的 .hmcl 文件夹中

[2012hzy]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces a feature to save custom game icons, adding a configuration setting, a settings UI, and logic to copy selected custom icons to a dedicated directory. The review feedback highlights a potential NoSuchFileException if the target directory does not exist when copying files, and points out a translation inconsistency in the Traditional Chinese localization file.

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[gemini-code-assist]

如果 game_icons 目录不存在，FileUtils.copyFile 可能会因为父目录不存在而抛出 NoSuchFileException。在复制文件之前，应该确保该目录已被创建。建议在解析目标路径前调用 Files.createDirectories(GAME_ICONS_DIR)。

Suggested change

	} else {
	dest = GAME_ICONS_DIR.resolve(selectedFile.getFileName());
	int i = 1;
	} else {
	Files.createDirectories(GAME_ICONS_DIR);
	dest = GAME_ICONS_DIR.resolve(selectedFile.getFileName());
	int i = 1;

[gemini-code-assist]

在繁体中文（I18N_zh.properties）中，settings.icon 使用了“圖示”，而新增的 settings.launcher.save_custom_game_icons 使用了“圖標”。为了保持用词一致性，建议将“圖標”改为“圖示”。

settings.launcher.save_custom_game_icons=保存自定義遊戲圖示