Continue row: only manga with something left after the last chapter read

GET /api/library returns `left` per manga: chapters after the newest saved
position that are unfinished, unread, or were last read more than 7 days
before it (a reread from the start). The continue row lists manga with
left > 0, so caught-up series drop out until a new chapter arrives.

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

docs/architecture.md

@@ -201,7 +201,7 @@ All requests and responses are JSON. POSTs require `Content-Type: application/js
 | `GET /api/reader-sessions` | user | `{ enabled, current, latestFrom, latest, sessions: [{ id, device, created, seen, current, locked, reader }] }` |
 | `POST /api/reader-sessions` `{id, action}` | user | `follow`: the session drops its own reader settings and follows the latest; `latest`: its settings become the latest |
 | `POST /api/password` `{old, new}` | user | Change password |
-| `GET /api/library` | user | Manga list with covers, counts, the user's read count, unread notifications, last read, and optional personal Reading Story aggregates |
+| `GET /api/library` | user | Manga list with covers, counts, the user's read count, unread notifications, last read, `left` (chapters after the newest saved position that are unfinished, unread, or last read over 7 days before it, i.e. a reread; 0 = caught up), and optional personal Reading Story aggregates |
 | `GET /api/manga?m=` | user | Manga details, books, chapters with ranked versions, progress, optional chapter-time summaries, and `continue` target |
 | `GET /api/chapter?m=&c=[&v=]` | user | Pages (`u, w, h, t, r`), direction, versions, prev/next, progress, `latest` (as in `/api/progress/latest`), optional Active Reading Clock summary, plus all books and chapters of the manga (with the user's read state) for the chapter picker. Also marks that chapter's notifications read |
 | `POST /api/progress` `{m, c, v, p, n, done, shift[, tab, seen]}` | user | Save the reading position. With `seen`, a save is refused (`{ok:false, stale:true, latest}`) when another tab saved a newer position of this manga since; otherwise `{ok:true, t}` |