feat: add envelope delete command and API endpoint

EnvelopeGenerator.Application/Envelopes/Commands/DeleteEnvelopeCommand.cs

@@ -0,0 +1,25 @@
+using System.ComponentModel.DataAnnotations;
+using EnvelopeGenerator.Domain.Constants;
+using MediatR;
+
+namespace EnvelopeGenerator.Application.Envelopes.Commands;
+
+public record DeleteEnvelopeResultDto(int EnvelopeId, EnvelopeStatus AppliedStatus, bool IsNoOp);
+
+public record DeleteEnvelopeCommand : IRequest<DeleteEnvelopeResultDto>
+{
+    [Required]
+    public int EnvelopeId { get; init; }
+
+    [Required]
+    [MinLength(1)]
+    public string Reason { get; init; } = string.Empty;
+
+    internal int UserId { get; private set; }
+
+    public DeleteEnvelopeCommand WithAuth(int userId)
+    {
+        UserId = userId;
+        return this;
+    }
+}