Migrate Show.Date from DateOnly to DateTime to support time of day

Removes DateOnly/DateTime conversion boilerplate from all Show endpoints
and adds the corresponding EF Core migration.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

PyroFetes/Endpoints/Show/GetAllShowsEndpoint.cs

@@ -22,7 +22,7 @@ public class GetAllShowsEndpoint(PyroFetesDbContext pyroFetesDbContext) : Endpoi
                 Place = s.Place,
                 Description = s.Description,
                 PyrotechnicImplementationPlan = s.PyrotechnicImplementationPlan,
-                Date = s.Date.HasValue ? s.Date.Value.ToDateTime(TimeOnly.MinValue) : null,
+                Date = s.Date,
                 CityId = s.CityId
             })
             .ToListAsync(ct);