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/lib/processors/check-watched-lists.processor.ts

@@ -0,0 +1,43 @@
+/**
+ * Component: Check Watched Lists Processor
+ * Documentation: documentation/features/watched-lists.md
+ *
+ * Dedicated processor for checking watched series and watched authors
+ * for new releases and auto-creating requests.
+ * Supports targeted processing of a single series/author for immediate sync.
+ */
+
+import { RMABLogger } from '../utils/logger';
+
+export interface CheckWatchedListsPayload {
+  jobId?: string;
+  scheduledJobId?: string;
+  /** If set, only process watched items for this user */
+  userId?: string;
+  /** If set, only process this specific series */
+  seriesAsin?: string;
+  /** If set, only process this specific author */
+  authorAsin?: string;
+}
+
+export async function processCheckWatchedLists(payload: CheckWatchedListsPayload): Promise<any> {
+  const { jobId, userId, seriesAsin, authorAsin } = payload;
+  const logger = RMABLogger.forJob(jobId, 'CheckWatchedLists');
+
+  const isTargeted = !!(userId && (seriesAsin || authorAsin));
+  logger.info(isTargeted
+    ? `Starting targeted watched lists check (user: ${userId}, series: ${seriesAsin || 'n/a'}, author: ${authorAsin || 'n/a'})...`
+    : 'Starting watched lists check...'
+  );
+
+  const { processWatchedLists } = await import('../services/watched-lists.service');
+  const stats = await processWatchedLists(logger, { userId, seriesAsin, authorAsin });
+
+  logger.info('Watched lists check complete', { stats });
+
+  return {
+    success: true,
+    message: isTargeted ? 'Targeted watched item checked' : 'Watched lists checked',
+    ...stats,
+  };
+}