Refactor VPN configuration handling to remove device limit management

- Updated the VPN configuration commands and handlers to eliminate the device limit parameter, simplifying the configuration process.
- Adjusted related API documentation to reflect the removal of device limit management, clarifying that this setting is now handled directly in the 3x-ui by node administrators.
- Enhanced the overall codebase by removing unnecessary device limit references across various components, ensuring a cleaner and more maintainable code structure.

frontend/src/routes/admin/roles.tsx

@@ -61,7 +61,7 @@ function AdminRolesPage() {
                 <td className="py-2">
                   {role.name} {role.isSystem && <Badge variant="outline">{t('admin.roles.system')}</Badge>}
                 </td>
-                <td className="py-2">{role.maxConfigs < 0 ? t('configs.deviceLimitUnlimited') : role.maxConfigs}</td>
+                <td className="py-2">{role.maxConfigs < 0 ? t('unlimited') : role.maxConfigs}</td>
                 <td className="py-2 text-right">
                   <Button size="sm" variant="outline" onClick={() => setEditing(role)}>
                     {t('admin.roles.edit')}