fix: HttpDownloadExecutor now calls ApplyAuthAsync for download requests

Download requests were missing the global auth provider and
ExtraHeaders (e.g. X-Tenant-Id) from HttpClientProvider, while
version validation and status reporting already applied them.
This caused tenant-scoped file downloads to fail when the server
requires X-Tenant-Id header.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: JusterZhu

src/c#/GeneralUpdate.Core/Download/Executors/HttpDownloadExecutor.cs

@@ -5,6 +5,7 @@
 using System.Threading;
 using System.Threading.Tasks;
 using GeneralUpdate.Core.Download.Abstractions;
+using GeneralUpdate.Core.Network;
 using GeneralUpdate.Core.Download.Models;
 
 namespace GeneralUpdate.Core.Download.Executors;
@@ -119,6 +120,11 @@ public async Task<DownloadResult> ExecuteAsync(
                     new System.Net.Http.Headers.AuthenticationHeaderValue(asset.AuthScheme, asset.AuthToken);
             }
 
+            // Apply global auth provider and extra headers (e.g. X-Tenant-Id) from HttpClientProvider.
+            // This ensures download requests carry the same auth context as version validation
+            // and status reporting requests.
+            await HttpClientProvider.ApplyAuthAsync(request, token).ConfigureAwait(false);
+
             using var cts = CancellationTokenSource.CreateLinkedTokenSource(token);
             cts.CancelAfter(_timeout);