Allow use of Touch ID instead of admin password when starting timer

[felipep]

Currently, when starting a timer in SelfControl, the app requires entering the Mac admin password. This can be inconvenient for users with devices that support Touch ID.

Feature Request:

Please add support for using Touch ID as an alternative authentication method when starting a SelfControl timer. This would improve the user experience and make the app feel more integrated with modern macOS authentication standards.

Additional context:

Touch ID works as an authentication method in many macOS system dialogs and apps. Adding this feature would align SelfControl with current macOS UX patterns.