Display flash/toast messages on all actions

Currently only a few actions actually display a flash message to provide feedback to performed actions, for example when publishing a page.

But many other actions do not display such feedback causing confusion or making the user believe something is not working, especially authorization checks (https://github.com/BeaconCMS/beacon/issues/521)

We need to use a component that is able to display messages after LV events and that do not require a navigation event. A good candidate is LiveToast https://x.com/src_rip/status/1791798294617755836

- [ ] Add LiveToast
- [ ] Replace existing flash messages with LiveToast calls
- [ ] Review existing actions (handle_event mostly) to add missing feedback