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.

prisma/schema.prisma

@@ -176,6 +176,7 @@ model Audiobook {
   year        Int?    // Release year extracted from releaseDate
   series      String? // Book series name (e.g., "The Mistborn Saga")
   seriesPart  String? @map("series_part") // Series position (e.g., "1", "1.5", "Book 1")
+  seriesAsin  String? @map("series_asin") // Audible series ASIN for linking to series detail page
 
   // Request tracking
   status String @default("requested") // requested, downloading, processing, completed, failed