Add series browsing, search, and detail UI

Introduce full support for Audible series exploration: API routes, frontend pages, components, hooks, and integrations. Key changes:

- Prisma: add Audiobook.seriesAsin for linking audiobooks to series detail pages.
- Backend: add /api/series/search and /api/series/[asin] routes that require auth; scrape Audible series data and enrich books with library availability.
- Integrations/services: add audible-series integration and update request/HTTP services to support the workflow.
- Frontend: add /series and /series/[asin] pages, new components (SeriesCard, SeriesGrid, SeriesDetailCard, SimilarSeriesRow) and wire them to a new useSeries hook; update AudiobookDetailsModal to show/link series; add Series link to Header.
- Misc: extend audiobook types with series fields and add seriesLabels to language-config for scraping.

These changes enable users to search for series, view series metadata and books, and navigate between audiobook and series detail pages.

src/components/layout/Header.tsx

@@ -166,6 +166,12 @@ export function Header() {
             >
               Authors
             </Link>
+            <Link
+              href="/series"
+              className="text-gray-700 dark:text-gray-300 hover:text-blue-600 dark:hover:text-blue-400 transition-colors"
+            >
+              Series
+            </Link>
             {showBookDate && (
               <Link
                 href="/bookdate"
@@ -277,6 +283,13 @@ export function Header() {
               >
                 Authors
               </Link>
+              <Link
+                href="/series"
+                onClick={() => setShowMobileMenu(false)}
+                className="px-3 py-2 text-gray-700 dark:text-gray-300 hover:bg-gray-100 dark:hover:bg-gray-700 rounded-md transition-colors"
+              >
+                Series
+              </Link>
               {showBookDate && (
                 <Link
                   href="/bookdate"