Bun on macOS 15+ (Darwin 24/25) returns the literal string "unknown" from
os.version() when uv_os_uname() cannot populate the version field. That
value was piped straight into the <workstation> block as `Kernel:
unknown`, and the model then guessed the OS glyph from the ambiguous
signal — displaying a Windows logo on Macs.
Fall back to `${os.type()} ${os.release()}` (uname -s + uname -r, e.g.
`Darwin 25.5.0`) whenever os.version() is empty or the literal
"unknown". Linux keeps its build string when Bun returns one.
Fixes#4141
roboomp