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/Models/Show.cs

@@ -8,7 +8,7 @@ public class Show
     [Required, MaxLength(100)] public string? Name { get; set; }
     [Required, MaxLength(120)] public string? Place { get; set; }
     [MaxLength(500)] public string? Description { get; set; }
-    public DateOnly? Date { get; set; }
+    public DateTime? Date { get; set; }
     
     // Link (path/URL/file name) to the pyrotechnic implementation plan
     [Required, MaxLength(500)] public string? PyrotechnicImplementationPlan { get; set; }