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>

public/app.css

@@ -387,6 +387,8 @@ main { max-width: 1200px; margin: 0 auto; padding: 16px; }
 .login input { width: 100%; }
 .saved { color: #7fd3a0; font-size: 13px; }
 .reading-data { margin-top: 16px; padding-top: 12px; border-top: 1px solid var(--line); }
+.reader-sessions { list-style: none; margin: 12px 0 0; padding: 0; }
+.reader-sessions li { display: grid; gap: 4px; padding: 10px 0; border-top: 1px solid var(--line); overflow-wrap: anywhere; }
 .reading-data > summary { cursor: pointer; font-weight: 600; }
 .reading-danger { margin-top: 14px; padding-top: 12px; border-top: 1px solid var(--line); }
 .reading-danger p { margin: 3px 0 8px; }