Function run_aur_ssh_setup 

pub fn run_aur_ssh_setup(overwrite_existing_host: bool) -> AurSshSetupResult

What: Run the guided AUR SSH setup flow.

Inputs:

• overwrite_existing_host: Whether to overwrite a conflicting existing host block.

Output:

• AurSshSetupResult with either completion report or explicit overwrite request.

Details:

• Creates ~/.ssh if missing.
• Generates ~/.ssh/aur_key via ssh-keygen if not present.
• Writes/updates minimal Host aur.archlinux.org block.