Expand test coverage to match specs

Endpoints/StateEndpoints.cs

@@ -80,6 +80,11 @@ public static class StateEndpoints
 
         group.MapPost("/me/name", async ([FromBody] SetNameRequest request, HttpContext ctx, AppDbContext db) =>
         {
+            if (request.Name?.Trim().Length > 16)
+            {
+                return Results.BadRequest(new { error = "Name is required and must be <= 16 characters." });
+            }
+
             var name = EndpointHelpers.TrimTo(request.Name, 16);
             if (string.IsNullOrWhiteSpace(name))
             {