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/update-versions-github.yml

@@ -11,8 +11,8 @@ permissions:
   pull-requests: write
 
 env:
-  SOURCES_FILE: frontend/public/json/version-sources.json
-  VERSIONS_FILE: frontend/public/json/versions.json
+  SOURCES_FILE: json/version-sources.json
+  VERSIONS_FILE: json/versions.json
 
 jobs:
   update-versions: