feat: install the Fortify authentication foundation

[ibourgeois]

Context

As a developer, I need an authentication baseline in place so user sessions and protected application flows can be built on a supported Laravel foundation.

Acceptance Criteria

• Fortify is installed and configured.
• Core authentication flows such as login and logout work.
• Any required setup or environment steps are documented.
• Authentication behavior is covered by tests where appropriate.

Notes

This should establish the auth foundation without overbuilding the surrounding product UI.

Out of Scope

• Advanced user management
• Final product-specific account workflows

[ibourgeois]

Resolved by the Fortify authentication foundation in #119. Fortify is installed and configured, login/logout/register/password reset flows are working, auth setup is documented, and the authentication behavior is covered by feature tests.