feat(auth): enhance authentication system with multi-user support and admin role management

- Implemented multi-user authentication with role-based access control.
- Added environment variables for initial admin user setup.
- Updated README and example environment file with new authentication options.
- Introduced user and system configuration models in the database schema.
- Enhanced authentication middleware to support user registration and role management.
- Updated frontend to handle new authentication flows, including admin user creation and role updates.

backend/.env.example

@@ -5,3 +5,9 @@ DATABASE_URL=file:/app/prisma/dev.db
 FRONTEND_URL=http://localhost:6767
 # Optional auth cookie settings: lax | strict | none
 AUTH_COOKIE_SAMESITE=lax
+# Optional auth bootstrap (creates initial admin)
+AUTH_USERNAME=admin
+AUTH_EMAIL=admin@example.com
+# If not set, a random password is generated and logged
+AUTH_PASSWORD=
+AUTH_MIN_PASSWORD_LENGTH=7