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>

.dockerignore

@@ -11,6 +11,7 @@
 !reading-analytics.js
 !reading-access.js
 !moments.js
+!reader-sessions.js
 !public/
 !public/**
 !greatest/