Make admin email login case-insensitive

[wakqasahmed]

Description

LoginController::credentials() passes the raw email input straight to the auth guard, so login is case-sensitive whenever the email column's collation is case-sensitive (e.g. Postgres, or MySQL with a _bin/case-sensitive collation) — a user created as User@example.com can't log in as user@example.com. Changed credentials() to match on LOWER(email) via a closure credential (Laravel's EloquentUserProvider has supported closures for custom query building since Laravel 8), so the match no longer depends on collation. Added an integration test that forces a case-sensitive collation on email for the duration of the test and restores it after — the default collation in this repo's own MySQL test DB is already case-insensitive, so a plain "log in with different case" test wouldn't have actually caught the regression.

Used AI assistance (Claude) to write and test this; reviewed the diff and ran the full LoginTest suite plus php-cs-fixer before opening.

Related Issues

Fixes #2789

[CLAassistant]

All committers have signed the CLA.

[wakqasahmed]

Hi @ifox — noticed this PR doesn't have a reviewer assigned yet — it's been sitting for a while, CI is green and it's mergeable. Would you (or whoever's best placed) be able to take a look, or point me to who should? Thanks!

[wakqasahmed]

Hi @ifox — circling back on this one — still no reviewer assigned, quiet for a while since the last activity. No pressure, just don't want it to get lost.