Incorrect "Letzter erfolgreicher Import" Date Displayed on Status Page After Restart

After restarting the application, the status page incorrectly shows the "Letzter erfolgreicher Import" date as `1 Jan. 1970, 01:00:00`, rather than the actual last successful import time. This issue occurs because the `ImportSummaryImpl` class, which is responsible for storing this information, is only application-scoped and is not saved to a database. As a result, it resets to a default state on application restart. The status page should display the actual last successful import timestamp after a restart, not a default date.