refactor: the kept versions are offered at a failed load, not in the menu

A list of timestamps in both file menus paid for itself only on the day
something went wrong, and it was in the way on every other. The entries
are gone; loadDocument now offers the versions where the browser copy has
actually failed the reader — newest first, one question each, and the one
taken up starts under the boot flag like any other document. The store
loses its reactive singleton with them.

README.md

@@ -31,7 +31,7 @@ EdenText is a web-based, powerful word processor for everything from quick notes
 > the way. It is tested — the full suite plus LibreOffice round-trip checks run
 > on every commit — but expect occasional bugs, and keep backups of documents
 > you care about. The browser copy also keeps the last three versions of the open
-> document — File ▸ Earlier versions puts one back.
+> document, and offers them if it ever fails to load one.
 
 [![EdenText editing a multi-column document](docs/screenshot.png)](https://edentext.app)
 Sample File from https://sample-files.com/