Adds callback failure logging

Adds logging for non-success status codes returned by the callback URL.

This improves debugging by providing visibility into callback failures, including the status code and a truncated response body.

src/LiquidCode.Tester.Worker/Services/CallbackService.cs

@@ -33,6 +33,14 @@ public class CallbackService : ICallbackService
             var content = new StringContent(json, Encoding.UTF8, "application/json");
 
             var httpResponse = await httpClient.PostAsync(callbackUrl, content);
+
+            if (!httpResponse.IsSuccessStatusCode)
+            {
+                var responseBody = await httpResponse.Content.ReadAsStringAsync();
+                _logger.LogWarning("Callback returned non-success status {StatusCode} with body: {Body}",
+                    (int)httpResponse.StatusCode, Truncate(responseBody, 2048));
+            }
+
             httpResponse.EnsureSuccessStatusCode();
 
             _logger.LogInformation("Status update sent successfully");
@@ -44,6 +52,16 @@ public class CallbackService : ICallbackService
         }
     }
 
+    private static string Truncate(string value, int maxLength)
+    {
+        if (string.IsNullOrEmpty(value) || value.Length <= maxLength)
+        {
+            return value;
+        }
+
+        return value.Substring(0, maxLength) + "…";
+    }
+
     private bool IsLogCallback(string callbackUrl)
     {
         if (string.IsNullOrWhiteSpace(callbackUrl))