One page. It checks the host, creates the tables and writes app/config.php.
app/config.php
Create an empty MySQL database and a user with full rights on it first, in cPanel or your host's panel.
Sign-in codes go out this way. SMTP is strongly preferred — mail() from shared hosting usually lands in spam, which looks exactly like broken verification.
Gmail needs an App password, not your normal password, and 2-step verification switched on.
Enables “Continue with Google” and backup to the user's own Drive. Create an OAuth client of type Web application whose Authorised redirect URI is <your app URL>/oauth.php, and enable the Google Drive API on the same project.
<your app URL>/oauth.php