Added an `[Authorize]` attribute with the "Sender" policy to restrict access to the `EnvelopeSenderPage.razor`. Updated the page title to "Umschläge" and added placeholder text for data loading.
Injected `EnvelopeService` and `IJSRuntime` to fetch and log active and completed envelopes. Introduced `_activeEnvelopes` and `_completedEnvelopes` fields to store fetched data. Configured `JsonSerializerOptions` for consistent JSON handling.
Implemented `OnInitializedAsync` to fetch data asynchronously, log results to the console, and handle errors gracefully.