Implement RBAC login and AdminLTE theming updates

[khoppenworth]

Summary

• add a PDO-backed Auth service with login/logout pages, RBAC guards, and sidebar navigation for public, staff, and admin users
• extend the database schema/sample data with a users table and document default credentials and role capabilities
• restyle the AdminLTE interface to use PANTONE® 294/200 accents, move interactions into a sidebar-driven layout, and gate import/export workflows by role

Testing

• for file in $(find . -name '*.php'); do php -l "$file"; done

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https://chatgpt.com/codex/tasks/task_e_68dd4168a31c832da3f0c499332338b3