Refactor Repository and update project dependencies

Added `SaveChangesAsync` to `IRepository` for async persistence.
Introduced AutoMapper and DbContext dependencies in `Repository`.
Simplified EF Core operations by removing `#if NET48` logic.
Replaced `Task.Run` with direct EF Core calls for .NET Framework.
Updated AutoMapper version for .NET 8 and added EF Core testing.
Suppressed AutoMapper vulnerability warning in project file.
Performed general cleanup and improved maintainability.

ECMJobRunner.Domain/Interfaces/IRepository.cs

@@ -90,5 +90,10 @@ namespace ECMJobRunner.Domain.Interfaces
         /// <param name="cancellationToken">Cancellation token</param>
         /// <returns>True if entity was found and deleted, false otherwise</returns>
         Task<bool> DeleteSingleAsync(Expression<Func<TEntity, bool>> predicate, CancellationToken cancellationToken = default);
+
+        /// <summary>
+        /// Save all changes asynchronously
+        /// </summary>
+        Task<int> SaveChangesAsync(CancellationToken cancellationToken = default);
     }
 }