Windows does not allow ':' in file or directory names. Make sure the log
file and the project directory do not contain ':' to prevent ENOENT
errors.

On Windows, URL.pathname returns a path with an extra leading '/' (e.g.
'\C:\Users\whatever'). This causes problems when using Bun.spawn(). Fix
these problems by using the right method instead of URL.pathname.

EmbedFS uses '/' always for file paths. It does not support '\' even on
Windows. Make sure we don't give EmbedFS a '\' path on Windows. This
lets the TUI find the theme files, avoiding crashes in various parts of
the code that assume a theme exists.