Reader settings per login session

Each sign-in keeps its own reader mode, zoom, page tone and skipping once
it changes one; sessions that never changed follow the latest set, and a
new sign-in starts from the session used last. Settings -> Reading shows
every session's state, lets a session follow the latest again or become
the latest, and turns the feature off for one shared set.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -50,6 +50,10 @@ Settings has **User** and **Admin** menu groups. User sections cover Reading, Re
 Notifications and Account. Admin sections cover Scraper, Server & library, Users & access, Collections &
 metadata and Service health. Only admins see administration ([settings navigation](docs/settings-navigation.md)).
 
+Reader settings (mode, zoom, page tone, skipping) are kept per sign-in: each device or browser keeps its own once you
+change one there, and a new sign-in starts from the one you used last. **Settings → Reading → Reader settings per
+session** shows every session's state and turns this off for one shared set ([details](docs/architecture.md#67-reader-settings-per-session)).
+
 ### Settings (environment variables)
 
 These configure the reader process. In Docker most are set for you by `docker-compose.yml`; the variables