fix(web-client): split DisplayName into FirstName/LastName for registration

apps/web-client-tpos-net/src/WebClientTpos.Client/Services/AuthService.cs

@@ -50,19 +50,22 @@ public class AuthService
     {
         try
         {
-            // EN: Build payload with FirstName/LastName from DisplayName (IAM requires these)
-            // VI: Tạo payload với FirstName/LastName từ DisplayName (IAM yêu cầu)
-            var parts = (dto.DisplayName ?? "User").Trim().Split(' ', 2);
+            // EN: Build payload with FirstName/LastName from form (IAM requires these)
+            // VI: Tạo payload với FirstName/LastName từ form (IAM yêu cầu)
             var payload = new
             {
                 dto.Email,
                 dto.Password,
-                FirstName = parts[0],
-                LastName = parts.Length > 1 ? parts[1] : parts[0],
-                DisplayName = dto.DisplayName
+                dto.FirstName,
+                dto.LastName
             };
 
-            var response = await _http.PostAsJsonAsync("/api/auth/register", payload);
+            // EN: Use PascalCase serialization to match backend RegisterUserCommand record params
+            // VI: Dùng PascalCase serialization để khớp với record params backend
+            var jsonOptions = new JsonSerializerOptions { PropertyNamingPolicy = null };
+            var jsonContent = JsonContent.Create(payload, options: jsonOptions);
+
+            var response = await _http.PostAsync("/api/auth/register", jsonContent);
             if (response.IsSuccessStatusCode)
             {
                 return (true, null);