A host from the web site; the same page kept once; deleting from the Notebooks chooser

From the development repository at 299f73d, 2026-10-11:
hosting from the site documented; a page loaded from a notebook and left
unchanged is not kept again; notebooks and pages are deleted from the
chooser, to the system's Trash (--trash); the Notebooks button.

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

docs/introduction.md

@@ -55,10 +55,11 @@ on their own computers.  The relay server that passes the messages cannot
 read them.  The invitation to a session carries the key, so only those
 who were invited can read the page.
 
-**Nothing to install for guests.**  A guest joins by opening a link in a
-web browser.  Someone who wants a notebook of real files on their own
-computer installs the small Kokkoja program instead; that is also how a
-host runs Kokkoja.
+**Nothing to install.**  A guest joins by opening a link in a web
+browser, and a host can start a session from the web site in the same
+way.  Someone who wants a notebook of real files on their own computer,
+a teacher with a notebook per student for instance, installs the small
+Kokkoja program instead.
 
 **Free software.**  Kokkoja is free and open-source.  Anyone can use it
 without paying, and nobody depends on a company's service.  It runs in
@@ -120,11 +121,13 @@ mind before reading on.
                               the client's files
 ```
 
-* **The host** runs the small Kokkoja program on their own computer.
-  It shows Kokkoja in the host's browser, at the address
+* **The host** in the picture runs the small Kokkoja program on their
+  own computer.  It shows Kokkoja in the host's browser, at the address
   `http://localhost:8760/`, and it keeps the host's notebooks as
   directories of files.  It must be running for as long as the host is
-  in a session; the browser alone cannot reach the notebooks.
+  in a session; the browser alone cannot reach the notebooks.  A host
+  can also do without it and start the session from the web site, like
+  guest A, with the notebooks in the browser.
 
 * **The server** does two things for everyone.  Its *relay* passes the
   participants' messages, which are encrypted before they leave each