Split SkillSaveContext and useSkillSaveManager into a separate file to
fix react-refresh/only-export-components lint error. Destructure
mutateAsync from useUpdateAppAssetFileContent for a stable callback
reference, preventing unnecessary useCallback cascade rebuilds. Extract
shared patchFileContentCache helper to unify setQueryData logic between
updateCachedContent and the collaboration event handler.
- use cleanup-based save on tab switch with stable fallback snapshots
- add fallback registry for metadata-only autosave consistency
- add autosave/save-manager tests
Centralize file save operations using Context/Provider pattern for better
maintainability. Add auto-save on tab switch, visibility change, page unload,
and component unmount.
