Add time record API endpoint and supporting infrastructure

Introduced a new TimeController with a POST endpoint to insert and retrieve the latest time record. Added ITimeRepository, TimeRepository, and TimeRecord entity. Implemented MediatR command and handler for time insertion. Updated ApplicationDbContext and DI configuration to support the new feature.

DbFirst.Application/Repositories/ITimeRepository.cs

@@ -0,0 +1,9 @@
+using DbFirst.Domain.Entities;
+
+namespace DbFirst.Application.Repositories;
+
+public interface ITimeRepository
+{
+    Task InsertAsync(CancellationToken cancellationToken = default);
+    Task<TimeRecord?> GetLastAsync(CancellationToken cancellationToken = default);
+}