feat: implement platform management system with authentication and dashboard

- Add PlatformUser model with roles (SUPER_ADMIN, ADMIN, SUPPORT)
- Implement platform authentication with NextAuth
- Create platform dashboard showing companies, users, and sessions
- Add platform API endpoints for company management
- Update landing page with SaaS design
- Include test improvements and accessibility updates

tests/unit/user-management.test.tsx

@@ -263,7 +263,7 @@ describe("UserManagementPage", () => {
 
       await waitFor(() => {
         const emailInput = screen.getByLabelText("Email") as HTMLInputElement;
-        
+
         fireEvent.change(emailInput, { target: { value: "invalid-email" } });
         fireEvent.blur(emailInput);