`rad-auth`: Activate identity only after successful passphrase check

[erak]

Motivation

If a user attempts to switch to another profile, the active profile will already be set to the selected one, even if the passphrase is not supplied and the selection flow aborted:

Your active profile is 792d1c65-4dcf-4d56-b296-27446491c90d

🌱 Authenticating as rad:git:hnrk8ki4e6m8rg3p1uchue3j6zxmda1f93m6f

ok Profile b172f291-f9ab-4990-b94e-738796026f50 activated
** Warning: Adding your radicle key to ssh-agent...
 ⤷ Passphrase · 

Check if it's possible to only activate after successful passphrase check (in case the key is not yet in the ssh-agent)