Refactor sender resolution and add history logging

Refactored sender email resolution into a new private async
method `ResolveSenderReferenceAsync` to improve code
reusability and readability. Replaced inline logic for
resolving sender references with this method.

Added a `CreateHistoryCommand` to log envelope creation
events, including envelope ID, sender reference, and status
(`EnvelopeCreated`). This enhances auditability and ensures
consistent event logging.

EnvelopeGenerator.Application/Envelopes/Commands/CreateEnvelopeCommandHandler.cs

@@ -104,6 +104,13 @@ public class CreateEnvelopeCommandHandler : IRequestHandler<CreateEnvelopeComman
                     UseAccessCode = false,
                     SendReminderEmails = false
                 }, cancel);
+
+            await Mediator.Send(new CreateHistoryCommand
+            {
+                EnvelopeId = envelope.Id,
+                UserReference = await ResolveSenderReferenceAsync(envelope, cancel),
+                Status = EnvelopeStatus.EnvelopeCreated
+            }, cancel);
         }
 
         await UpsertDocumentAsync(envelope.Id, request.Document, now, cancel);
@@ -121,6 +128,22 @@ public class CreateEnvelopeCommandHandler : IRequestHandler<CreateEnvelopeComman
         return _mapper.Map<EnvelopeDto>(envelope);
     }
 
+    private async Task<string> ResolveSenderReferenceAsync(Envelope envelope, CancellationToken cancel)
+    {
+        if (!string.IsNullOrWhiteSpace(envelope.User?.Email))
+            return envelope.User.Email;
+
+        var senderEmail = await Repository.Query
+            .Where(e => e.Id == envelope.Id)
+            .Select(e => e.User.Email)
+            .FirstOrDefaultAsync(cancel);
+
+        if (string.IsNullOrWhiteSpace(senderEmail))
+            throw new BadRequestException("Envelope sender email is missing.");
+
+        return senderEmail;
+    }
+
     private async Task UpsertDocumentAsync(int envelopeId, CreateEnvelopeDocumentDto? document, DateTime now, CancellationToken cancel)
     {
         if (document is null || string.IsNullOrWhiteSpace(document.DataAsBase64))
@@ -338,9 +361,7 @@ public class CreateEnvelopeCommandHandler : IRequestHandler<CreateEnvelopeComman
             e.ChangedWhen = changedWhen;
         }, e => e.Id == envelope.Id, cancel);
 
-        var userReference = envelope.User?.Email;
-        if (string.IsNullOrWhiteSpace(userReference))
-            throw new BadRequestException("Envelope sender email is missing.");
+        var userReference = await ResolveSenderReferenceAsync(envelope, cancel);
 
         await Mediator.Send(new CreateHistoryCommand
         {