When the copilot binary is found in PATH but exec fails (e.g., due to
unusual characters like parentheses in the path on Windows), append a
hint suggesting the user run `copilot` directly without `gh`.
The hint is only shown when the binary was already present on the host,
not when it was freshly downloaded and installed by `gh`.
Closescli/cli#13106
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
