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.Infrastructure/RecDbContext.cs

@@ -103,7 +103,11 @@ public class RecDbContext(DbContextOptions<RecDbContext> options) : DbContext(op
             b.Property(e => e.PostprocessingQuery).HasColumnName("POSTPROCESSING_QUERY");
         });
 
-        modelBuilder.Entity<HeaderQueryResult>().HasNoKey();
+        modelBuilder.Entity<HeaderQueryResult>(b =>
+        {
+            b.HasNoKey();
+            b.Property(e => e.RawHeader).HasColumnName("REQUEST_HEADER");
+        });
 
         modelBuilder.Entity<BodyQueryResult>(b =>
         {