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)

docs/AI.md

@@ -705,7 +705,7 @@ cleanup_lxc
 - [ ] `motd_ssh`, `customize`, `cleanup_lxc` at the end
 - [ ] No custom download/version-check logic
 - [ ] No default `(Patience)` text in msg_info labels
-- [ ] JSON metadata file created in `frontend/public/json/<appname>.json`
+- [ ] JSON metadata file created in `json/<appname>.json`
 
 ---
 
@@ -727,7 +727,7 @@ cleanup_lxc
 
 ## <20> JSON Metadata Files
 
-Every application requires a JSON metadata file in `frontend/public/json/<appname>.json`.
+Every application requires a JSON metadata file in `json/<appname>.json`.
 
 ### JSON Structure