feat(security): library visibility enforced at the source; per-library series; annotation ownership; admin user creation

The family-lens hardening: library_visibility was only enforced where
file bytes flowed (download/reader/OPDS) — metadata surfaces leaked
hidden libraries to any authenticated account, and registration was
open by default with no admin-side user creation.

- Series are grouped PER LIBRARY now (same name in two libraries =
  two entries: manga adaptations / LN splits no longer merge);
  /api/series aggregates only the requester's VISIBLE libraries and
  /api/series/books REQUIRES a visible library_id (breaking contract;
  web + app clients updated in the same change).
- /api/media-items, item detail, and the reader content endpoints
  (chapters/panels/outline/THUMBNAILS — page images leaked unguarded
  next to a gated GetPage) all enforce the visible set; resolveLibrary
  no longer honors a hand-typed library_id outside the visible set.
- Annotation/note/bookmark mutations (update/delete/tombstone, sync
  LWW paths incl. conflict resolution) carry ownership predicates:
  another account's bare row id is a 404, not a silent delete.
- Admin user creation: POST /api/auth/users (AdminMiddleware) + a
  Create User card in the admin Users UI — accounts stay creatable
  with self-service registration OFF, which is now the schema default
  (fresh installs; the first-admin bootstrap exception is unchanged).
- Tests: series contract re-pinned (per-library, visibility 403s),
  new ownership + admin-create integration suites, OPDS all=1 test
  now passes an explicit page size (shared-DB growth made the fresh
  books fall off page 1), device-cap helper switched to the admin
  endpoint.

web/src/series.ts

@@ -4,6 +4,7 @@ import { initLibrarySwitcher, switchWithTransition } from "./library-switcher";
 
 interface SeriesItem {
   name: string;
+  library_id: string;
   book_count: number;
   total_in_series: number;
   cover_paths: string[];
@@ -11,7 +12,7 @@ interface SeriesItem {
 }
 
 function renderSeriesCard(series: SeriesItem): string {
-  const href = `/series/detail?name=${encodeURIComponent(series.name)}`;
+  const href = `/series/detail?name=${encodeURIComponent(series.name)}&library_id=${encodeURIComponent(series.library_id ?? "")}`;
   const coverCount = series.cover_paths.length;
   const coverClass = `cover-count-${coverCount}`;