Users can now register beacon monitors on the settings page. Each
monitor gets a unique random token the remote program will use to
authenticate its reports. Name is the only user-supplied field for
now; more will be added as the monitor protocol is defined.
Also adds :gen_smtp to deps. Swoosh's SMTP adapter depends on
:mimemail which lives in that package, and production was 500'ing
when trying to send confirmation emails without it.
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
