- Remove auto-confirmation on registration (register_user and register_user_with_organization)
- Add deliver_user_confirmation_instructions/2 and confirm_user/1 to Accounts context
- Add verify_email_token_query/2 and by_user_and_contexts_query/2 to UserToken
- Make deliver_confirmation_email public in UserNotifier
- Send confirmation email after registration in both flows
- Block unconfirmed users at password login with helpful message
- Add UserConfirmationController with confirm/resend routes
- Add resend confirmation link to login page
- Update test fixtures to confirm users after registration
