Fold email columns into init.sql, drop the admin/admin demo mention

Fresh installs (docker compose up -d --build, exactly what the README
tells a new self-hoster to run) never got the email/must_set_email/
self_registered_at columns added in migration 006 - only init.sql runs
automatically, migrations always need a manual step, and this one
never got folded into the base schema. A genuine first-time clone
would have broken immediately on login. Verified with a real fresh
volume: seed superadmin now correctly walks through forced password
change -> forced email set -> dashboard, no manual migration needed.

Also: qr.ensembia.com's README/About text still pointed at the
shared admin/admin demo login - replaced with a link to register.php
now that self-registration is live (the shared account has been
removed from the live instance).

README.md

@@ -8,8 +8,8 @@ of the original [PHP Dynamic Qr code](https://github.com/giandonatoinverso/PHP-D
 project by Giandonato Inverso, built on [AdminLTE](https://adminlte.io/).
 
 - **Try it free:** [qr.ensembia.com](https://qr.ensembia.com) - fully functional OSS test
-  instance. Self-service signup isn't live yet, so log in with the temporary shared demo
-  account `admin` / `admin` in the meantime.
+  instance. [Register your own free account](https://qr.ensembia.com/register.php)
+  (email + a self-hosted CAPTCHA, no third-party service) - no shared demo login needed.
 - **Commercial VIP edition:** the ability to give sub-users the ability to create
   QR codes as well, from their own (sub)account. If you have a bigger organisation,
   having more users being able to create new QR codes delegates your workload. To