Refactor admin/user isolation logic and model methods

Moved admin/user isolation checks and related methods from Domain and NotificationGroup models to User model for better separation of concerns. Replaced direct database queries in controllers and services with new model methods. Added methods for assigning unassigned domains/groups, searching domains, and clearing old notification logs. Updated views for improved UI consistency.

app/Services/NotificationService.php

@@ -276,9 +276,8 @@ class NotificationService
     public function notifyAdminsUpgrade(string $fromVersion, string $toVersion, int $migrationsCount): void
     {
         try {
-            $pdo = \Core\Database::getConnection();
-            $stmt = $pdo->query("SELECT id FROM users WHERE role = 'admin'");
-            $admins = $stmt->fetchAll(\PDO::FETCH_ASSOC);
+            $userModel = new \App\Models\User();
+            $admins = $userModel->getAllAdmins();
             
             foreach ($admins as $admin) {
                 $this->notifySystemUpgrade($admin['id'], $fromVersion, $toVersion, $migrationsCount);