feat(sender): support draft editing flow in sender pages

EnvelopeGenerator.Server/EnvelopeGenerator.Server/Services/EnvelopeReceiverPageDataService.cs

@@ -49,6 +49,14 @@ public class EnvelopeReceiverPageDataService(
             : throw new NotFoundException($"Document for envelope {envelopeId} not found.");
     }
 
+    /// <summary>
+    /// Loads the full document DTO (including receiver elements) for the authenticated sender.
+    /// </summary>
+    public async Task<DocumentDto> GetDocumentDetailsOfSenderAsync(ClaimsPrincipal user, int envelopeId, CancellationToken cancellationToken = default)
+    {
+        return await mediator.Send(new ReadDocumentQuery(EnvelopeId: envelopeId, UserId: user.SenderId()), cancellationToken);
+    }
+
     /// <summary>
     /// Loads the current receiver's signature placeholders.
     /// </summary>