[BF] Public access level (0) not always granted

[Rawk]

User::AUTH_PUBLIC is an int, so the config value needs to be cast to an int before checking with ===.

This fixes a problem where having GRAPHER_ACCESS_CUSTOMER=0 in .env is not giving public access. Probably fixes other cases too.

I have not run the unit tests and psalm. If you think it is needed for this change, i have to take some time to set it up first.

In addition to the above, I have:

• ensured unit tests all run without error
• ran psalm and corrected any static analysis issues
• ensured all relevant template output is escaped to avoid XSS attached with <?= $t->ee( $data ) ?> or equivalent
• ensured appropriate checks against user privilege / resources accessed
• API calls (particular for add/edit/delete/toggle) are not implemented with GET and use CSRF tokens to avoid CSRF attacks

[barryo]

Given that these are all prechecked with is_numeric(), this looks fine. Thanks @Rawk. GitHub will run the unit tests once I move to main.