Add resilient upload queue and client health

src/OCSentinelCli/Transport/N8nUploadClient.cs

@@ -38,17 +38,31 @@ internal sealed class N8nUploadClient
         request.Headers.Add("X-ATN-Payload-SHA256", payloadHash);
         request.Headers.Add("X-ATN-Signature", signature);
 
-        using HttpResponseMessage response = httpClient.Send(request);
-        string responseText = response.Content.ReadAsStringAsync().GetAwaiter().GetResult();
-
-        return new UploadResult
+        try
         {
-            Success = response.IsSuccessStatusCode,
-            StatusCode = (int)response.StatusCode,
-            Message = string.IsNullOrWhiteSpace(responseText) ? response.ReasonPhrase ?? string.Empty : responseText,
-            Nonce = nonce,
-            PayloadSha256 = payloadHash
-        };
+            using HttpResponseMessage response = httpClient.Send(request);
+            string responseText = response.Content.ReadAsStringAsync().GetAwaiter().GetResult();
+
+            return new UploadResult
+            {
+                Success = response.IsSuccessStatusCode,
+                StatusCode = (int)response.StatusCode,
+                Message = string.IsNullOrWhiteSpace(responseText) ? response.ReasonPhrase ?? string.Empty : responseText,
+                Nonce = nonce,
+                PayloadSha256 = payloadHash
+            };
+        }
+        catch (Exception exception) when (exception is HttpRequestException or TaskCanceledException)
+        {
+            return new UploadResult
+            {
+                Success = false,
+                StatusCode = 0,
+                Message = exception.Message,
+                Nonce = nonce,
+                PayloadSha256 = payloadHash
+            };
+        }
     }
 
     private static string ComputeSha256(string value)