ci: upgrade GitHub Actions to support Node.js 24 (#951)

* ci: upgrade GitHub Actions to support Node.js 24

- pnpm/action-setup: v4 → v5
- actions/upload-artifact: v4 → v6
- actions/download-artifact: v4 → v6
- sync.yaml: replace inactive aormsby/Fork-Sync-With-Upstream-action with gh repo sync

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* ci: replace softprops/action-gh-release with gh release CLI

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix(ci): use gh release upload instead of create for existing releases

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

.github/workflows/frontend_pagefunction_deploy.yaml

@@ -39,7 +39,7 @@ jobs:
         with:
           node-version: 22
 
-      - uses: pnpm/action-setup@v4
+      - uses: pnpm/action-setup@v5
         name: Install pnpm
         with:
           version: 10