feat(repository): Methode ReadLastByReceiver zu IEnvelopeReceiverRepository und EnvelopeReceiverRepository hinzugefügt

- Methode `ReadLastByReceiver` zum Interface `IEnvelopeReceiverRepository` hinzugefügt.
- Methode `ReadLastByReceiver` in `EnvelopeReceiverRepository` implementiert, um den letzten `EnvelopeReceiver` anhand der E-Mail-Adresse abzurufen.

EnvelopeGenerator.Infrastructure/Repositories/EnvlopeReceiverRepository.cs

@@ -1,5 +1,4 @@
 using DigitalData.Core.Infrastructure;
-using DigitalData.UserManager.Infrastructure.Repositories;
 using EnvelopeGenerator.Domain.Entities;
 using EnvelopeGenerator.Infrastructure.Contracts;
 using Microsoft.EntityFrameworkCore;
@@ -76,5 +75,10 @@ namespace EnvelopeGenerator.Infrastructure.Repositories
 
             return await query.Include(er => er.Envelope).Include(er => er.Receiver).ToListAsync();
         }
+
+        public async Task<EnvelopeReceiver?> ReadLastByReceiver(string email)
+        {
+            return await _dbSet.Where(er => er.Receiver!.EmailAddress == email).LastOrDefaultAsync();
+        }
     }
 }