- Update UserNotifier to use t_email() helper for all email content
- Extract 4 email subjects and 4 email bodies to emails domain:
* Update email instructions
* Log in instructions
* Confirmation instructions
* Reset password instructions
- Replace string interpolation with Gettext bindings (%{email}, %{url})
- Auto-populate English translations (msgstr = msgid)
- All emails now ready for future internationalization
First module migration complete per design plan.
