Enhanced the `SenderEditorPage.razor` by injecting the `EnvelopeReceiverService` to manage envelope receivers. Updated the UI to include a remove button for each receiver, invoking the new `RemoveReceiverAsync` method. This method handles the deletion of receivers from both the UI and the server.
Modified `ReceiverDraft` and `SignatureFieldDraft` models to include `ReceiverId` and `ReceiverDraftId` for better tracking. Updated logic for identifying receivers without signature fields and creating receiver commands to use these new identifiers.
Added `DeleteAsync` method in `EnvelopeReceiverService.cs` to send DELETE requests for removing receivers. Updated `envelope-viewer.css` to style the new remove button with distinct appearance and hover effects.