* refactor(deep-link)!: return Error::Execute when an OS command fails to run
On Linux, `register`, `unregister` and `is_registered` now fail with the
new `Error::Execute(command, io_error)` variant when `xdg-mime` or
`update-desktop-database` cannot be spawned, instead of logging and
returning the raw `Error::Io`. This is the change deferred to v3 in #2970.
* docs(deep-link): unregister does not run OS commands
