Generated Accounts context, User schema, and controllers via
phx.gen.auth. Adapted it for password-only login with required
email confirmation:
- Users have callsign (unique, uppercased), name, email, password
- Registration form fields: callsign, name, email, password, confirm
- Magic-link login path removed; login is email + password only
- After register, a confirmation email is sent and login is blocked
until the account is confirmed via the token URL
- Confirmation link logs the user in on first use
- SMTP2GO configured as the outgoing mailer in k8s prod
