feat: Add authentication system and admin panel

- Add User model with authentication
- Create JWT-based auth service
- Add login page with admin/admin default credentials
- Create admin panel with user management, settings, and site configuration
- Move settings to admin section (admin only)
- Change search page from multi-site checkboxes to single site selector
- Add logout functionality to layout
- Protect routes with authentication

pyproject.toml

@@ -25,6 +25,7 @@ dependencies = [
     "slowapi",
     "beautifulsoup4",
     "lxml",
+    "pyjwt",
 ]
 
 [build-system]