- Create admin-session lib with sign/verify helpers using HMAC-SHA256
- Add admin login API that checks hardcoded super/admin credentials
and DB-stored admin users with bcrypt password comparison
- Add admin logout API to clear session cookie
- Add change-password API for admin self-service password changes
- Create admin login page with Macedonian UI
- Update middleware to protect /admin/* and /api/admin/* routes
with admin session check, bypassing Clerk auth
