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/create-ready-for-testing-message.yml

@@ -59,19 +59,19 @@ jobs:
               FILES=(
                 "ct/${TITLE}.sh"
                 "install/${TITLE}-install.sh"
-                "frontend/public/json/${TITLE}.json"
+                "json/${TITLE}.json"
               )
               ;;
             vm)
               FILES=(
                 "vm/${TITLE}.sh"
-                "frontend/public/json/${TITLE}.json"
+                "json/${TITLE}.json"
               )
               ;;
             addon)
               FILES=(
                 "tools/addon/${TITLE}.sh"
-                "frontend/public/json/${TITLE}.json"
+                "json/${TITLE}.json"
               )
               ;;
             pve)
@@ -122,7 +122,7 @@ jobs:
           JSON_FILE=""
           case "$SCRIPT_TYPE" in
             ct|vm|addon)
-              JSON_FILE="frontend/public/json/${TITLE}.json"
+              JSON_FILE="json/${TITLE}.json"
               ;;
           esac