fix: add missing exit statements in integration callback and OAuth files

auth/callback_microsoft.php

@@ -95,3 +95,4 @@ $saveStmt->execute([$user['id'], $accessToken, $refreshToken, json_encode($newSe
 // 8. Succesvol terugkeren naar de Integraties Hub
 header('Location: /integrations.php?success=' . urlencode("Microsoft Outlook succesvol gekoppeld als {$accountEmail}!"));
 exit;
+

auth/oauth_microsoft.php

@@ -40,3 +40,4 @@ $_SESSION['ms_oauth_user_id'] = $user['id'];
 $authUrl = microsoft_get_auth_url($clientId, $redirectUri, $tenantId, $state);
 header("Location: {$authUrl}");
 exit;
+