Refactor EnvelopeType handling and improve validation

Removed AutoMapper dependency in `ReadEnvelopeTypesQueryHandler` and replaced it with manual projection to address null-materialization issues. Updated `EnvelopeType` entity properties to nullable types to align with the database schema. Adjusted computed properties to handle null values gracefully.

Enhanced `SenderEditorPage` with authentication checks, improved handling of reminder and expiry settings, and added validation for user input. Introduced `NormalizeSettings` and `ValidateSettings` methods to ensure consistent and valid configurations. Refactored checkbox value parsing for better reliability.

Injected `AuthService` and `IStringLocalizer` for authentication and localization support. Improved error messaging and localized validation errors. Performed minor code cleanup and refactoring for better readability and maintainability.

EnvelopeGenerator.Application/EnvelopeTypes/Queries/ReadEnvelopeTypesQuery.cs

@@ -1,6 +1,5 @@
 using EnvelopeGenerator.Application.Common.Dto;
 using MediatR;
-using AutoMapper;
 using DigitalData.Core.Abstraction.Application.Repository;
 using EnvelopeGenerator.Domain.Entities;
 using Microsoft.EntityFrameworkCore;
@@ -18,17 +17,14 @@ public record ReadEnvelopeTypesQuery : IRequest<IEnumerable<EnvelopeTypeDto>>;
 public class ReadEnvelopeTypesQueryHandler : IRequestHandler<ReadEnvelopeTypesQuery, IEnumerable<EnvelopeTypeDto>>
 {
     private readonly IRepository<EnvelopeType> _repository;
-    private readonly IMapper _mapper;
 
     /// <summary>
     /// 
     /// </summary>
     /// <param name="repository"></param>
-    /// <param name="mapper"></param>
-    public ReadEnvelopeTypesQueryHandler(IRepository<EnvelopeType> repository, IMapper mapper)
+    public ReadEnvelopeTypesQueryHandler(IRepository<EnvelopeType> repository)
     {
         _repository = repository;
-        _mapper = mapper;
     }
 
     /// <summary>
@@ -39,7 +35,28 @@ public class ReadEnvelopeTypesQueryHandler : IRequestHandler<ReadEnvelopeTypesQu
     /// <returns></returns>
     public async Task<IEnumerable<EnvelopeTypeDto>> Handle(ReadEnvelopeTypesQuery request, CancellationToken cancellationToken)
     {
-        var types = await _repository.Query.ToListAsync(cancellationToken);
-        return _mapper.Map<IEnumerable<EnvelopeTypeDto>>(types);
+        // TODO: Temporary manual projection to avoid null-materialization crashes from legacy nullable DB columns in EnvelopeType.
+        // Revisit and switch to AutoMapper query projection (ProjectTo) after schema nullability and mapping contracts are stabilized.
+        return await _repository.Query
+            .AsNoTracking()
+            .Select(t => new EnvelopeTypeDto
+            {
+                Id = t.Id,
+                Title = t.Title ?? string.Empty,
+                Language = string.IsNullOrWhiteSpace(t.Language) ? "de-DE" : t.Language,
+                ExpiresDays = t.ExpiresDays,
+                CertificationType = (int?)t.CertificationType,
+                UseAccessCode = t.UseAccessCode,
+                FinalEmailToCreator = (int?)t.FinalEmailToCreator,
+                FinalEmailToReceivers = (int?)t.FinalEmailToReceivers,
+                AddedWhen = t.AddedWhen,
+                ChangedWhen = t.ChangedWhen,
+                ExpiresWarningDays = t.ExpiresWarningDays,
+                SendReminderEmails = t.SendReminderEmails,
+                FirstReminderDays = t.FirstReminderDays,
+                ReminderIntervalDays = t.ReminderIntervalDays,
+                ContractType = t.ContractType
+            })
+            .ToListAsync(cancellationToken);
     }
-}
+}