feat(backoffice): add reading progress management, series page, and live search

- API: add POST /series/mark-read to batch mark all books in a series
- API: add GET /series cross-library endpoint with search, library and status filters
- API: add library_id to SeriesItem response
- Backoffice: mark book as read/unread button on book detail page
- Backoffice: mark series as read/unread button on series cards
- Backoffice: new /series top-level page with search and filters
- Backoffice: new /libraries/[id]/series/[name] series detail page
- Backoffice: opacity on fully read books and series cards
- Backoffice: live search with debounce on books and series pages
- Backoffice: reading status filter on books and series pages
- Fix $2 -> $1 parameter binding in mark-series-read SQL

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/backoffice/app/components/MobileNav.tsx

@@ -6,9 +6,9 @@ import Link from "next/link";
 import { NavIcon } from "./ui";
 
 type NavItem = {
-  href: "/" | "/books" | "/libraries" | "/jobs" | "/tokens" | "/settings";
+  href: "/" | "/books" | "/series" | "/libraries" | "/jobs" | "/tokens" | "/settings";
   label: string;
-  icon: "dashboard" | "books" | "libraries" | "jobs" | "tokens" | "settings";
+  icon: "dashboard" | "books" | "series" | "libraries" | "jobs" | "tokens" | "settings";
 };
 
 const HamburgerIcon = () => (