- asyncBtn now returns fn().finally(...) so callers can await/chain it
- Move re-fetch calls inside try/catch in core.js and permissions.js so
network errors from fetchAndRenderStalePerms / fetchAndRender* are
caught instead of escaping as unhandled rejections
- clearStaleAgent returns the asyncBtn promise so the function is
properly awaitable when a button is present
- Update asyncBtn doc comment to reflect the return-value contract