feat(release): ship self-updating Velopack packages on GitHub Releases

Publish-Windows.ps1 now packs the smoke-tested folder with the pinned vpk
CLI (.config/dotnet-tools.json, 1.2.0 to match the Velopack package) into
velopack/: Setup.exe, Portable.zip, the full nupkg, releases.win.json and
RELEASES, checked for the full package and the portable layout and hashed
into OpenNest.vX.Y.Z.velopack.sha256. The release workflow uploads them
with the candidate.

With no feed URL set, installed copies now check GitHub Releases (full
releases only) instead of skipping update checks; a URL in Options still
selects a self-hosted feed. Deploy-OpenNest.ps1 uses the pinned vpk.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.github/workflows/windows-release.yml

@@ -96,6 +96,11 @@ jobs:
           path: |
             artifacts/*.zip
             artifacts/*.sha256
+            artifacts/velopack/OpenNest-win-Setup.exe
+            artifacts/velopack/OpenNest-win-Portable.zip
+            artifacts/velopack/*-full.nupkg
+            artifacts/velopack/releases.win.json
+            artifacts/velopack/RELEASES
           if-no-files-found: error
           retention-days: 14
           compression-level: 0