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/app/api/user/watched-authors/[id]/route.ts

@@ -0,0 +1,52 @@
+/**
+ * Component: Watched Author Delete Route
+ * Documentation: documentation/features/watched-lists.md
+ */
+
+import { NextRequest, NextResponse } from 'next/server';
+import { requireAuth, AuthenticatedRequest } from '@/lib/middleware/auth';
+import { prisma } from '@/lib/db';
+import { RMABLogger } from '@/lib/utils/logger';
+
+const logger = RMABLogger.create('API.WatchedAuthors');
+
+/**
+ * DELETE /api/user/watched-authors/[id]
+ * Remove an author from the user's watch list (ownership check)
+ */
+export async function DELETE(
+  request: NextRequest,
+  { params }: { params: Promise<{ id: string }> }
+) {
+  return requireAuth(request, async (req: AuthenticatedRequest) => {
+    try {
+      if (!req.user) {
+        return NextResponse.json({ error: 'Unauthorized' }, { status: 401 });
+      }
+
+      const { id } = await params;
+
+      const watched = await prisma.watchedAuthor.findUnique({
+        where: { id },
+      });
+
+      if (!watched) {
+        return NextResponse.json({ error: 'Watched author not found' }, { status: 404 });
+      }
+
+      // Ownership check
+      if (watched.userId !== req.user.id) {
+        return NextResponse.json({ error: 'Forbidden' }, { status: 403 });
+      }
+
+      await prisma.watchedAuthor.delete({ where: { id } });
+
+      logger.info(`User ${req.user.id} stopped watching author "${watched.authorName}" (${watched.authorAsin})`);
+
+      return NextResponse.json({ success: true });
+    } catch (error) {
+      logger.error('Failed to delete watched author', { error: error instanceof Error ? error.message : String(error) });
+      return NextResponse.json({ error: 'Failed to delete watched author' }, { status: 500 });
+    }
+  });
+}