refactor: Replace dynamic MIME type loading with static array

[tourze]

将 MIME 类型映射从动态文件加载改为静态数组定义，带来以下好处：

• 消除运行时文件 I/O 操作，提升启动性能
• 减少文件系统依赖，提高代码可移植性
• 简化代码维护，MIME 类型映射直接可见
• 避免文件读取失败的潜在风险
• 减少不必要的函数导入

删除了 mime.types 文件和 initMimeTypeMap() 方法，将所有 MIME 类型 映射直接定义在 $mimeTypeMap 静态数组中。

🤖 Generated with Claude Code

[joanhey]

I think that is better to be in a separate file.

But we can change the mime.types file copied from nginx, to a PHP file that return the array.
Also the array need to be separated by type with a blank line, to read and modify easily.

PD: actually we need to add image/avif