Add series fields to audiobooks and update related logic

Introduces 'series' and 'seriesPart' fields to the Audiobook model and database schema. Updates API routes, file organization, and path template utilities to support series metadata. Enhances chapter merging logic, improves notification backend testing, and expands test coverage for admin and API routes.

tests/lib/hooks/useAudiobooks.test.tsx

@@ -0,0 +1,109 @@
+/**
+ * Component: Audiobooks Hooks Tests
+ * Documentation: documentation/frontend/components.md
+ */
+
+// @vitest-environment jsdom
+
+import React from 'react';
+import { render, screen } from '@testing-library/react';
+import { beforeEach, describe, expect, it, vi } from 'vitest';
+
+const useSWRMock = vi.hoisted(() => vi.fn());
+const authenticatedFetcherMock = vi.hoisted(() => vi.fn());
+
+vi.mock('swr', () => ({
+  default: useSWRMock,
+}));
+
+vi.mock('@/lib/utils/api', () => ({
+  authenticatedFetcher: authenticatedFetcherMock,
+}));
+
+const HookProbe = ({ label, value }: { label: string; value: any }) => (
+  <div data-testid={label}>{JSON.stringify(value)}</div>
+);
+
+describe('useAudiobooks hooks', () => {
+  beforeEach(() => {
+    useSWRMock.mockReset();
+    authenticatedFetcherMock.mockReset();
+    vi.resetModules();
+  });
+
+  it('builds the popular audiobooks endpoint and returns data', async () => {
+    useSWRMock.mockReturnValue({
+      data: { audiobooks: [{ asin: 'a1' }], totalPages: 3, totalCount: 30, hasMore: true },
+      error: null,
+      isLoading: false,
+    });
+
+    const { useAudiobooks } = await import('@/lib/hooks/useAudiobooks');
+
+    const Probe = () => {
+      const result = useAudiobooks('popular', 10, 2);
+      return <HookProbe label="popular" value={result} />;
+    };
+
+    render(<Probe />);
+
+    expect(useSWRMock).toHaveBeenCalledWith(
+      '/api/audiobooks/popular?page=2&limit=10',
+      authenticatedFetcherMock,
+      expect.objectContaining({ dedupingInterval: 60000 })
+    );
+
+    const parsed = JSON.parse(screen.getByTestId('popular').textContent || '{}');
+    expect(parsed.audiobooks).toHaveLength(1);
+    expect(parsed.totalPages).toBe(3);
+    expect(parsed.hasMore).toBe(true);
+  });
+
+  it('skips search when the query is empty', async () => {
+    useSWRMock.mockReturnValue({ data: null, error: null, isLoading: false });
+
+    const { useSearch } = await import('@/lib/hooks/useAudiobooks');
+
+    const Probe = () => {
+      const result = useSearch('', 1);
+      return <HookProbe label="search" value={result} />;
+    };
+
+    render(<Probe />);
+
+    expect(useSWRMock).toHaveBeenCalledWith(
+      null,
+      authenticatedFetcherMock,
+      expect.objectContaining({ dedupingInterval: 30000 })
+    );
+
+    const parsed = JSON.parse(screen.getByTestId('search').textContent || '{}');
+    expect(parsed.isLoading).toBeFalsy();
+  });
+
+  it('requests audiobook details when an ASIN is provided', async () => {
+    useSWRMock.mockReturnValue({
+      data: { audiobook: { asin: 'a2', title: 'Details' } },
+      error: null,
+      isLoading: false,
+    });
+
+    const { useAudiobookDetails } = await import('@/lib/hooks/useAudiobooks');
+
+    const Probe = () => {
+      const result = useAudiobookDetails('a2');
+      return <HookProbe label="details" value={result} />;
+    };
+
+    render(<Probe />);
+
+    expect(useSWRMock).toHaveBeenCalledWith(
+      '/api/audiobooks/a2',
+      authenticatedFetcherMock,
+      expect.objectContaining({ dedupingInterval: 300000 })
+    );
+
+    const parsed = JSON.parse(screen.getByTestId('details').textContent || '{}');
+    expect(parsed.audiobook.asin).toBe('a2');
+  });
+});