Enhance email template handling and documentation

- Added XML documentation to the `Handle` method in `UpdateEmailTemplateCommandHandler`.
- Improved readability in `ReadEmailTemplateQueryHandler` by storing the mapped response in a variable.
- Updated properties in `ReadEmailTemplateResponse` to be mutable and renamed `Type` to `Name` with a type change from `int` to `string`.
- Added data annotations in `EmailTemplate` for `AddedWhen` and introduced a new nullable `ChangedWhen` property.
- Included necessary using directives for data annotations in `EmailTemplate.cs`.

EnvelopeGenerator.Application/EmailTemplates/Commands/Update/UpdateEmailTemplateCommandHandler.cs

@@ -24,6 +24,14 @@ public class UpdateEmailTemplateCommandHandler : IRequestHandler<UpdateEmailTemp
         _repository = repository;
     }
 
+    /// <summary>
+    /// 
+    /// </summary>
+    /// <param name="request"></param>
+    /// <param name="cancel"></param>
+    /// <returns></returns>
+    /// <exception cref="InvalidOperationException"></exception>
+    /// <exception cref="NotFoundException"></exception>
     public async Task Handle(UpdateEmailTemplateCommand request, CancellationToken cancel)
     {
         var temp = (request.EmailTemplateQuery?.Id is int id

EnvelopeGenerator.Application/EmailTemplates/Queries/Read/ReadEmailTemplateQueryHandler.cs

@@ -45,6 +45,8 @@ public class ReadEmailTemplateQueryHandler : IRequestHandler<ReadEmailTemplateQu
                 ? await _repository.ReadByNameAsync(type)
                 : throw new InvalidOperationException("Either a valid integer ID or a valid EmailTemplateType must be provided in the request.");
 
-        return temp is null ? null : _mapper.Map<ReadEmailTemplateResponse>(temp);
+        var res = _mapper.Map<ReadEmailTemplateResponse>(temp);
+
+        return res;
     }
 }

EnvelopeGenerator.Application/EmailTemplates/Queries/Read/ReadEmailTemplateResponse.cs

@@ -8,17 +8,17 @@ public class ReadEmailTemplateResponse
     /// <summary>
     /// Die eindeutige Kennung der E-Mail-Vorlage.
     /// </summary>
-    public int Id { get; init; }
+    public int Id { get; set; }
 
     /// <summary>
-    /// Der Typ der E-Mail-Vorlage.
+    /// Name des Typs
     /// </summary>
-    public int Type { get; init; }
+    public required string Name { get; set; }
 
     /// <summary>
     /// Das Datum und die Uhrzeit, wann die Vorlage hinzugefügt wurde.
     /// </summary>
-    public DateTime AddedWhen { get; init; }
+    public DateTime AddedWhen { get; set; }
 
     /// <summary>
     /// Der Inhalt (Body) der E-Mail-Vorlage. Kann null sein.

EnvelopeGenerator.Domain/Entities/EmailTemplate.cs

@@ -1,4 +1,5 @@
 using DigitalData.Core.Abstractions;
+using System.ComponentModel;
 using System.ComponentModel.DataAnnotations;
 using System.ComponentModel.DataAnnotations.Schema;
 
@@ -20,5 +21,13 @@ namespace EnvelopeGenerator.Domain.Entities
 
         [Column("SUBJECT", TypeName = "nvarchar(512)")]
         public string? Subject { get; set; }
+
+        [Required]
+        [Column("ADDED_WHEN", TypeName = "datetime")]
+        [DefaultValue("GETDATE()")]
+        public DateTime AddedWhen { get; set; }
+
+        [Column("CHANGED_WHEN", TypeName = "datetime")]
+        public DateTime? ChangedWhen { get; set; }
     }
 }