refactor: move json/ to top-level, remove frontend/, update workflows

- Move frontend/public/json/ to json/ (top-level)
- Update all workflow path references to json/
- Delete frontend-cicd.yml workflow
- Delete frontend/ directory entirely
- Clean up .gitattributes (remove frontend entries)

.github/workflows/bak/get-versions-from-gh.yaml

@@ -47,7 +47,7 @@ jobs:
           git config --global user.email "github-actions[bot]@users.noreply.github.com"
           git config --global user.name "GitHub Actions[bot]"
           git checkout -b update_versions || git checkout update_versions
-          git add frontend/public/json/versions.json
+          git add json/versions.json
           if git diff --cached --quiet; then
             echo "No changes detected."
             echo "changed=false" >> "$GITHUB_ENV"