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/hooks/useWatchedAuthors.ts

@@ -0,0 +1,119 @@
+/**
+ * Component: Watched Authors Hook
+ * Documentation: documentation/features/watched-lists.md
+ */
+
+'use client';
+
+import { useState } from 'react';
+import useSWR, { mutate } from 'swr';
+import { useAuth } from '@/contexts/AuthContext';
+import { fetchWithAuth } from '@/lib/utils/api';
+
+export interface WatchedAuthorItem {
+  id: string;
+  authorAsin: string;
+  authorName: string;
+  coverArtUrl: string | null;
+  lastCheckedAt: string | null;
+  createdAt: string;
+}
+
+const fetcher = (url: string) =>
+  fetchWithAuth(url).then((res) => res.json());
+
+export function useWatchedAuthors() {
+  const { accessToken } = useAuth();
+
+  const endpoint = accessToken ? '/api/user/watched-authors' : null;
+
+  const { data, error, isLoading } = useSWR(
+    endpoint,
+    fetcher,
+    { refreshInterval: 60000 }
+  );
+
+  return {
+    authors: (data?.authors || []) as WatchedAuthorItem[],
+    isLoading,
+    error,
+  };
+}
+
+export function useAddWatchedAuthor() {
+  const { accessToken } = useAuth();
+  const [isLoading, setIsLoading] = useState(false);
+  const [error, setError] = useState<string | null>(null);
+
+  const addAuthor = async (authorAsin: string, authorName: string, coverArtUrl?: string) => {
+    if (!accessToken) throw new Error('Not authenticated');
+
+    setIsLoading(true);
+    setError(null);
+
+    try {
+      const response = await fetchWithAuth('/api/user/watched-authors', {
+        method: 'POST',
+        headers: { 'Content-Type': 'application/json' },
+        body: JSON.stringify({ authorAsin, authorName, coverArtUrl }),
+      });
+
+      const data = await response.json();
+
+      if (!response.ok) {
+        throw new Error(data.message || data.error || 'Failed to watch author');
+      }
+
+      // Revalidate watched authors list
+      mutate((key) => typeof key === 'string' && key.includes('/api/user/watched-authors'));
+
+      return data.author as WatchedAuthorItem;
+    } catch (err) {
+      const message = err instanceof Error ? err.message : 'Unknown error';
+      setError(message);
+      throw err;
+    } finally {
+      setIsLoading(false);
+    }
+  };
+
+  return { addAuthor, isLoading, error };
+}
+
+export function useDeleteWatchedAuthor() {
+  const { accessToken } = useAuth();
+  const [isLoading, setIsLoading] = useState(false);
+  const [error, setError] = useState<string | null>(null);
+
+  const deleteAuthor = async (id: string) => {
+    if (!accessToken) throw new Error('Not authenticated');
+
+    setIsLoading(true);
+    setError(null);
+
+    try {
+      const response = await fetchWithAuth(`/api/user/watched-authors/${id}`, {
+        method: 'DELETE',
+      });
+
+      const data = await response.json();
+
+      if (!response.ok) {
+        throw new Error(data.message || data.error || 'Failed to unwatch author');
+      }
+
+      // Revalidate watched authors list
+      mutate((key) => typeof key === 'string' && key.includes('/api/user/watched-authors'));
+
+      return true;
+    } catch (err) {
+      const message = err instanceof Error ? err.message : 'Unknown error';
+      setError(message);
+      throw err;
+    } finally {
+      setIsLoading(false);
+    }
+  };
+
+  return { deleteAuthor, isLoading, error };
+}