ZAYN User Management - v5

Added:
- Admin panel: users.php user/customer management dashboard
- User detail: profile, email, username, phone, role, status, password reset
- Admin roles and per-section permissions
- First/owner admin is protected and always has full access
- Customer/admin blocking with forced session invalidation
- Force logout by incrementing session_version
- Login by email or username
- Last login time/IP
- Internal admin note
- Admin activity history
- Create customer/admin accounts
- Delete non-protected accounts
- Search, role/status filters and pagination
- Database migration adds username, permissions, security metadata and user_activity
- All admin pages are permission guarded; sidebar hides unavailable sections
