Add watched series/authors feature

Introduce watched lists for series and authors end-to-end.

- Add DB migration to create watched_series and watched_authors tables with indexes and foreign keys.
- Implement API routes: GET/POST for listing/adding and DELETE by id for both /api/user/watched-series and /api/user/watched-authors. Validation, ownership checks, and immediate targeted job triggers are included.
- Add client hooks (useWatchedSeries, useWatchedAuthors) with add/delete helpers and SWR revalidation.
- Add UI components: WatchButton (toggle/confirm) and WatchedListsSection for profile display and removal UX.
- Add processor (check-watched-lists.processor) and service (watched-lists.service) to scrape Audible, deduplicate, check library ownership, and auto-create requests; supports targeted checks for newly watched items.
- Include tests for the watched-lists service.

These changes implement the watched-lists feature to let users watch series/authors and have the system automatically detect and request new releases.

src/components/series/SeriesDetailCard.tsx

@@ -11,6 +11,7 @@
 import React, { useState } from 'react';
 import Image from 'next/image';
 import { SeriesDetail } from '@/lib/hooks/useSeries';
+import { WatchSeriesButton } from '@/components/ui/WatchButton';
 
 interface SeriesDetailCardProps {
   series: SeriesDetail;
@@ -91,20 +92,27 @@ export function SeriesDetailCard({ series, squareCovers = false }: SeriesDetailC
           </div>
         )}
 
-        {/* Audible Link */}
-        {series.audibleUrl && (
-          <a
-            href={series.audibleUrl}
-            target="_blank"
-            rel="noopener noreferrer"
-            className="mt-3 inline-flex items-center gap-1.5 text-sm text-gray-500 dark:text-gray-400 hover:text-indigo-600 dark:hover:text-indigo-400 transition-colors"
-          >
-            View on Audible
-            <svg className="w-3.5 h-3.5" fill="none" stroke="currentColor" viewBox="0 0 24 24">
-              <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M10 6H6a2 2 0 00-2 2v10a2 2 0 002 2h10a2 2 0 002-2v-4M14 4h6m0 0v6m0-6L10 14" />
-            </svg>
-          </a>
-        )}
+        {/* Actions row: Audible link + Watch button */}
+        <div className="mt-3 flex flex-wrap items-center justify-center sm:justify-start gap-3">
+          {series.audibleUrl && (
+            <a
+              href={series.audibleUrl}
+              target="_blank"
+              rel="noopener noreferrer"
+              className="inline-flex items-center gap-1.5 text-sm text-gray-500 dark:text-gray-400 hover:text-indigo-600 dark:hover:text-indigo-400 transition-colors"
+            >
+              View on Audible
+              <svg className="w-3.5 h-3.5" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+                <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M10 6H6a2 2 0 00-2 2v10a2 2 0 002 2h10a2 2 0 002-2v-4M14 4h6m0 0v6m0-6L10 14" />
+              </svg>
+            </a>
+          )}
+          <WatchSeriesButton
+            seriesAsin={series.asin}
+            seriesTitle={series.title}
+            coverArtUrl={series.books[0]?.coverArtUrl}
+          />
+        </div>
 
         {/* Description */}
         {series.description && (