Tooltips in the Notebooks chooser

From the development repository at e819bc4.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

docs/guest.md

@@ -218,6 +218,10 @@ doing anything.  Where it is saved depends on how you joined.
 
 **Notebooks** in the toolbar opens a chooser that shows your notebooks
 and small pictures of the pages kept in them, wherever they are kept.
+Rest the pointer on a page for a second and its facts appear: the first
+text on it, when it was last changed, who wrote on it, what is on it
+and the size of the sheet; on a notebook, how many pages it keeps and
+from when, when it was last written in, and where it is.
 There you can delete pages and notebooks you no longer want: mark them
 with the × at their left, then press **Delete** twice.  In the browser
 a deleted page is gone for good; with the Kokkoja program it goes to the

docs/implementation.md

@@ -177,7 +177,10 @@ a page of another session in the notebook.  Nothing is copied if the
 page is blank or the same page is already kept in that notebook; a
 page loaded from a notebook and left unchanged is therefore not kept
 again, although the file names it as a new page.  A kept page or a
-whole notebook can be deleted from the Notebooks chooser; the local
+whole notebook can be deleted from the Notebooks chooser, whose
+tooltips describe each page (from the page file itself, which the
+chooser fetches for the picture) and each notebook (from the listing,
+which names the pages and says when each was last written); the local
 program moves it to the system's Trash (the freedesktop Trash on
 Linux, with the info file the file manager wants for putting it back;
 `~/.Trash` on macOS) unless `--trash` says otherwise, and the