feat(config): add DefaultEmail to configuration files for payment processing

- Introduced DefaultEmail field in cms-config.yaml, appsettings.json, and appsettings.Staging.json to standardize email handling in payment requests.
- Updated TwentyCardPaymentService to utilize DefaultEmail when no email is provided in the request, enhancing error handling and user experience.

src/CMSMicroservice.Infrastructure/Services/Payment/TwentyCardPaymentService.cs

@@ -19,6 +19,7 @@ public class TwentyCardPaymentService : IPaymentGatewayService
     private readonly string _terminalId;
     private readonly string _terminalUsername;
     private readonly string _terminalPassword;
+    private readonly string _defaultEmail;
 
     private static readonly JsonSerializerOptions JsonOptions = new()
     {
@@ -43,8 +44,11 @@ public class TwentyCardPaymentService : IPaymentGatewayService
             ?? throw new InvalidOperationException("TwentyCard:TerminalUsername is not configured.");
         _terminalPassword = configuration["TwentyCard:TerminalPassword"]
             ?? throw new InvalidOperationException("TwentyCard:TerminalPassword is not configured.");
+        _defaultEmail = configuration["TwentyCard:DefaultEmail"] ?? "info@kbs2.ir";
 
         _httpClient.BaseAddress = new Uri(baseUrl.TrimEnd('/') + "/");
+        if (!_httpClient.DefaultRequestHeaders.Contains("Accept"))
+            _httpClient.DefaultRequestHeaders.TryAddWithoutValidation("Accept", "application/json");
         _logger.LogInformation("TwentyCard payment service initialized. BaseUrl={BaseUrl}", baseUrl);
     }
 
@@ -72,13 +76,13 @@ public class TwentyCardPaymentService : IPaymentGatewayService
                 ["mobile"] = request.Mobile ?? string.Empty,
                 ["invoice"] = invoice,
                 ["callback"] = request.CallbackUrl,
-                ["description"] = request.Description ?? string.Empty
+                ["description"] = request.Description ?? string.Empty,
+                // بدون email درگاه ۲۰کارت به‌جای validation، HTTP 500 برمی‌گرداند
+                ["email"] = ResolveEmail(request.Email)
             });
 
-            if (!string.IsNullOrWhiteSpace(request.Email))
-                content.Add(new StringContent(request.Email), "email");
             if (!string.IsNullOrWhiteSpace(request.NationalId))
-                content.Add(new StringContent(request.NationalId), "national_id");
+                AddFormField(content, "national_id", request.NationalId);
 
             _logger.LogInformation(
                 "TwentyCard payment request: Amount={Amount} Toman, User={UserId}, Invoice={Invoice}",
@@ -241,10 +245,27 @@ public class TwentyCardPaymentService : IPaymentGatewayService
     {
         var form = new MultipartFormDataContent();
         foreach (var (key, value) in fields)
-            form.Add(new StringContent(value ?? string.Empty), key);
+            AddFormField(form, key, value ?? string.Empty);
         return form;
     }
 
+    /// <summary>
+    /// شبیه curl --form: بدون Content-Type روی هر part ( بعضی بک‌اندهای PHP با charset=utf-8 می‌شکنند).
+    /// </summary>
+    private static void AddFormField(MultipartFormDataContent form, string name, string value)
+    {
+        var part = new StringContent(value ?? string.Empty);
+        part.Headers.ContentType = null;
+        form.Add(part, name);
+    }
+
+    private string ResolveEmail(string? email)
+    {
+        if (!string.IsNullOrWhiteSpace(email) && email.Contains('@', StringComparison.Ordinal))
+            return email.Trim();
+        return _defaultEmail;
+    }
+
     private sealed class TwentyCardRequestResponse
     {
         public string? Message { get; set; }