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.Application/Envelopes/Commands/CreateEnvelopeCommand.cs

@@ -1,5 +1,4 @@
-using DigitalData.Core.Abstraction.Application.Repository;
-using EnvelopeGenerator.Application.Common.Dto;
+using EnvelopeGenerator.Application.Common.Dto;
 using EnvelopeGenerator.Application.Common.Interfaces.SQLExecutor;
 using MediatR;
 using System.ComponentModel.DataAnnotations;
@@ -13,23 +12,29 @@ namespace EnvelopeGenerator.Application.Envelopes.Commands;
 /// </summary>
 public record CreateEnvelopeCommand : IRequest<EnvelopeDto?>
 {
+    public int? EnvelopeId { get; init; }
+
     /// <summary>
     /// Der Titel des Umschlags. Dies ist ein Pflichtfeld.
     /// </summary>
-    [Required]
-    public required string Title { get; set; }
+    public string? Title { get; set; }
 
     /// <summary>
     /// Die Nachricht, die im Umschlag enthalten sein soll. Dies ist ein Pflichtfeld.
     /// </summary>
-    [Required]
-    public required string Message { get; set; }
+    public string? Message { get; set; }
 
     /// <summary>
     /// Gibt an, ob die Zwei-Faktor-Authentifizierung für den Umschlag aktiviert ist. Standardmäßig false.
     /// </summary>
     public bool TFAEnabled { get; set; } = false;
 
+    public bool Send { get; init; }
+
+    public CreateEnvelopeDocumentDto? Document { get; init; }
+
+    public List<CreateEnvelopeReceiverDto> Receivers { get; init; } = new();
+
     /// <summary>
     /// ID des Absenders
     /// </summary>
@@ -55,4 +60,14 @@ public record CreateEnvelopeCommand : IRequest<EnvelopeDto?>
     [JsonIgnore]
     [NotMapped]
     public bool UseSQLExecutor { get; set; } = true;
-}
+}
+
+public record CreateEnvelopeDocumentDto(string DataAsBase64);
+
+public record CreateEnvelopeFieldDto(double X, double Y, int Page);
+
+public record CreateEnvelopeReceiverDto(
+    string EmailAddress,
+    string? Name,
+    string? PhoneNumber,
+    List<CreateEnvelopeFieldDto> Fields);