feat: Implement client authentication and pre-fill functionality

- Added AuthController for client login and token management.
- Introduced AuthGate for handling authentication state and login UI.
- Updated API to support fetching client data for pre-filling forms.
- Modified App.vue to pre-fill client information if logged in.
- Enhanced client model to include username and password fields.
- Created migration for adding username and password to clients table.
- Added utility for generating secure usernames and passwords.
- Updated frontend to handle client tokens for pre-filling checkout forms.
- Removed old CSS file and updated HTML references to new assets.
- Added StatsOverview widget for displaying client and quote statistics.
- Improved error handling and user feedback in the login process.

backoffice/config/preventivi.php

@@ -6,4 +6,7 @@ return [
 
     // URL base dell'app cliente (per link nelle email admin).
     'frontend_cliente_url' => env('APP_FRONTEND_CLIENTE_URL', 'http://localhost:5199'),
+
+    // Durata (in giorni) della sessione di login del configuratore.
+    'configurator_session_days' => (int) env('CONFIGURATOR_SESSION_DAYS', 30),
 ];