Move RawHeader column mapping to Fluent API config

Removed data annotation from HeaderQueryResult and mapped RawHeader to REQUEST_HEADER using Fluent API in RecDbContext. Centralizes entity configuration in the DbContext.

src/ReC.Domain/Entities/HeaderQueryResult.cs

@@ -1,9 +1,6 @@
-using System.ComponentModel.DataAnnotations.Schema;
-
-namespace ReC.Domain.Entities;
+namespace ReC.Domain.Entities;
 
 public class HeaderQueryResult
 {
-    [Column("REQUEST_HEADER")]
     public string? RawHeader { get; init; }
 }