feat: refactor HTTP client setup for Github and Forgejo services

- Centralized HTTP client configuration for `GithubService` and `ForgejoService` using `AddHttpClient`.
- Enhanced maintainability by moving Forgejo token and base URL setup into DI-configured HTTP clients.
- Fixed `forgejoInstance` validation logic and adjusted release selection to prioritize the first non-prerelease.

Services/SyncService.cs

@@ -36,7 +36,7 @@ public class SyncService(
         var (owner, name) = ParseGithubUrl(repo.GithubUrl);
 
         var githubReleases = await githubService.FetchRepoReleasesAsync(owner, name, token);
-        var githubRelease = githubReleases.LastOrDefault(r => !r.Prerelease);
+        var githubRelease = githubReleases.FirstOrDefault(r => !r.Prerelease);
         if (githubRelease is null)
         {
             logger.LogWarning("{Owner}/{Name}: no GitHub release found, skipping", owner, name);
@@ -44,7 +44,7 @@ public class SyncService(
         }
 
         var forgejoReleases = await forgejoService.FetchRepoReleasesAsync(owner, name, token);
-        var forgejoRelease = forgejoReleases.LastOrDefault(r => !r.Prerelease);
+        var forgejoRelease = forgejoReleases.FirstOrDefault(r => !r.Prerelease);
 
         var releaseId = await ResolveReleaseIdAsync(owner, name, githubRelease, forgejoRelease, token);