Four-stat overview widget (users, stations, oil prediction, API errors)
with 30s polling registered on the admin panel dashboard.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Runs is_admin migration, adds AdminSeeder for the admin user, registers
it in DatabaseSeeder, adds admin() factory state to UserFactory, and
adds AdminAccessTest covering both forbidden and ok cases.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
