add UserRendererService and improve errors

Foxnouns.Backend/Services/MemberRendererService.cs

@@ -0,0 +1,18 @@
+using Foxnouns.Backend.Database;
+using Foxnouns.Backend.Database.Models;
+
+namespace Foxnouns.Backend.Services;
+
+public class MemberRendererService(DatabaseContext db)
+{
+    public PartialMember RenderPartialMember(Member member) => new(member.Id, member.Name,
+        member.DisplayName, member.Bio, member.Names, member.Pronouns);
+
+    public record PartialMember(
+        Snowflake Id,
+        string Name,
+        string? DisplayName,
+        string? Bio,
+        IEnumerable<FieldEntry> Names,
+        IEnumerable<Pronoun> Pronouns);
+}