v2.12.2: fix(auth): Support IPv6 addresses in session storage IP column

The `StorageEntity::$ip` column was `VARCHAR(15)`, suitable only for IPv4. Requests from IPv6 clients would fail to create or extend sessions with a "Data too long for column 'ip'" error in strict SQL mode.

This change increases the column length to `VARCHAR(45)` to accommodate IPv6 addresses and includes upgrade instructions in the README.