feat: integrate Forgejo API for release synchronization and asset download

Services/ReleaseAssetDownloadService.cs

@@ -0,0 +1,14 @@
+namespace ForgejoReleaseSync.Services;
+
+public class ReleaseAssetDownloadService(HttpClient httpClient)
+{
+    public async Task<string> DownloadReleaseAssetAsync(Uri url)
+    {
+        var fileName = Path.GetFileName(url.AbsoluteUri);
+        var filePath = Path.Combine(Path.GetTempPath(), fileName);
+        await using Stream resource = await httpClient.GetStreamAsync(url);
+        await using FileStream fs = new FileStream(filePath, FileMode.OpenOrCreate);
+        await resource.CopyToAsync(fs, 8192);
+        return filePath;
+    }
+}