Add error log management and bulk admin actions

Introduces error log tracking with new ErrorLog model, controller, views, and migration. Adds admin UI for viewing, resolving, and deleting errors. Implements bulk actions for users and notification groups, refactors domain filtering/pagination, and centralizes admin access checks using Auth::requireAdmin().

core/Auth.php

@@ -69,5 +69,37 @@ class Auth
             exit;
         }
     }
+
+    /**
+     * Require admin role (redirect with error if not admin)
+     */
+    public static function requireAdmin(): void
+    {
+        // First ensure user is authenticated
+        self::require();
+        
+        // Then check for admin role
+        if (!isset($_SESSION['role']) || $_SESSION['role'] !== 'admin') {
+            $_SESSION['error'] = 'Access denied. Admin privileges required.';
+            header('Location: /');
+            exit;
+        }
+    }
+
+    /**
+     * Check if current user is admin
+     */
+    public static function isAdmin(): bool
+    {
+        return isset($_SESSION['role']) && $_SESSION['role'] === 'admin';
+    }
+
+    /**
+     * Get current user's role
+     */
+    public static function role(): ?string
+    {
+        return $_SESSION['role'] ?? null;
+    }
 }