Fix duplicate logging for successful email confirmation

[aduth]

🛠 Summary of changes

Fixes an issue where we currently log the 'User Registration: Email Confirmation' event twice for every account registration.

Email confirmation happens across two controllers, which each individually validate the incoming confirmation token. Since the analytics were logged as part of this shared validation, it was being logged twice.

The solution is to move the analytics logging to happen only after the first successful validation.

📜 Testing Plan

Verify you see a single 'User Registration: Email Confirmation' event when confirming an email address for a new account:

1. Run make watch_events in a separate terminal process
2. Go to http://localhost:3000
3. Click "Create an account"
4. Enter an email address
5. Confirm Rules of Use
6. Click "Submit"
7. In the email received, click "Confirm email address"
8. Observe in make watch_events process output that there is only a single event for 'User Registration: Email Confirmation'