refactor(envelope): consolidate draft flow into upsert command

- extend CreateEnvelopeCommand to support draft updates and send intent

- merge draft save logic into CreateEnvelopeCommandHandler and remove duplicate handler

- add DocReceiverElement writer abstraction and infrastructure registration for SQL-based field upserts

EnvelopeGenerator.Infrastructure/Writers/DocReceiverElementWriter.cs

@@ -0,0 +1,56 @@
+#if NET
+using EnvelopeGenerator.Application.Common.Interfaces;
+using EnvelopeGenerator.Domain.Entities;
+using Microsoft.EntityFrameworkCore;
+
+namespace EnvelopeGenerator.Infrastructure.Writers;
+
+public class DocReceiverElementWriter(EGDbContext dbContext) : IDocReceiverElementWriter
+{
+    public Task DeleteByDocumentAndReceiverAsync(int documentId, int receiverId, CancellationToken cancellationToken = default)
+    {
+        return dbContext.Database.ExecuteSqlInterpolatedAsync(
+            $"DELETE FROM [dbo].[TBSIG_DOCUMENT_RECEIVER_ELEMENT] WHERE [DOCUMENT_ID] = {documentId} AND [RECEIVER_ID] = {receiverId}",
+            cancellationToken);
+    }
+
+    public Task InsertAsync(DocReceiverElement element, CancellationToken cancellationToken = default)
+    {
+        return dbContext.Database.ExecuteSqlInterpolatedAsync($@"
+INSERT INTO [dbo].[TBSIG_DOCUMENT_RECEIVER_ELEMENT]
+       ([DOCUMENT_ID]
+       ,[RECEIVER_ID]
+       ,[ELEMENT_TYPE]
+       ,[POSITION_X]
+       ,[POSITION_Y]
+       ,[WIDTH]
+       ,[HEIGHT]
+       ,[REQUIRED]
+       ,[READ_ONLY]
+       ,[PAGE]
+       ,[ADDED_WHEN]
+       ,[FULL_NAME]
+       ,[POSITION]
+       ,[PLACE]
+       ,[TOOLTIP]
+       ,[ANNOTATION_INDEX])
+ VALUES ({element.DocumentId}
+       ,{element.ReceiverId}
+       ,{element.ElementType}
+       ,{element.X}
+       ,{element.Y}
+       ,{element.Width}
+       ,{element.Height}
+       ,{element.Required}
+       ,{element.ReadOnly}
+       ,{element.Page}
+       ,{element.AddedWhen}
+       ,{element.FullName}
+       ,{element.Position}
+       ,{element.Place}
+       ,{element.Tooltip}
+       ,{element.AnnotationIndex})",
+            cancellationToken);
+    }
+}
+#endif