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/components/bookdate/BookPickerModal.test.tsx

@@ -0,0 +1,158 @@
+/**
+ * Component: BookDate Book Picker Modal Tests
+ * Documentation: documentation/features/bookdate.md
+ */
+
+// @vitest-environment jsdom
+
+import React from 'react';
+import { fireEvent, render, screen, waitFor } from '@testing-library/react';
+import { afterEach, describe, expect, it, vi } from 'vitest';
+
+const books = [
+  { id: 'book-1', title: 'First Book', author: 'Author One', coverUrl: null },
+  { id: 'book-2', title: 'Second Book', author: 'Author Two', coverUrl: null },
+];
+
+describe('BookPickerModal', () => {
+  afterEach(() => {
+    vi.unstubAllGlobals();
+    localStorage.clear();
+  });
+
+  it('loads books and confirms the selection', async () => {
+    const fetchMock = vi.fn().mockResolvedValue({
+      ok: true,
+      json: async () => ({ books }),
+    });
+    vi.stubGlobal('fetch', fetchMock);
+    localStorage.setItem('accessToken', 'token-123');
+    const onConfirm = vi.fn();
+    const onClose = vi.fn();
+    const { BookPickerModal } = await import('@/components/bookdate/BookPickerModal');
+
+    render(
+      <BookPickerModal
+        isOpen={true}
+        onClose={onClose}
+        selectedIds={[]}
+        onConfirm={onConfirm}
+        maxSelection={5}
+      />
+    );
+
+    await waitFor(() => {
+      expect(fetchMock).toHaveBeenCalledWith('/api/bookdate/library', {
+        headers: { Authorization: 'Bearer token-123' },
+      });
+    });
+
+    const firstBookButton = await screen.findByRole('button', { name: /First Book/ });
+    fireEvent.click(firstBookButton);
+
+    fireEvent.click(screen.getByRole('button', { name: /Confirm Selection/ }));
+
+    expect(onConfirm).toHaveBeenCalledWith(['book-1']);
+    expect(onClose).toHaveBeenCalled();
+  });
+
+  it('disables additional selections once the max is reached', async () => {
+    const fetchMock = vi.fn().mockResolvedValue({
+      ok: true,
+      json: async () => ({ books }),
+    });
+    vi.stubGlobal('fetch', fetchMock);
+    localStorage.setItem('accessToken', 'token-456');
+    const { BookPickerModal } = await import('@/components/bookdate/BookPickerModal');
+
+    render(
+      <BookPickerModal
+        isOpen={true}
+        onClose={vi.fn()}
+        selectedIds={[]}
+        onConfirm={vi.fn()}
+        maxSelection={1}
+      />
+    );
+
+    const firstBookButton = await screen.findByRole('button', { name: /First Book/ });
+    fireEvent.click(firstBookButton);
+
+    expect(screen.getByText(/Maximum reached/)).toBeInTheDocument();
+
+    const secondBookButton = screen.getByRole('button', { name: /Second Book/ });
+    expect(secondBookButton).toBeDisabled();
+  });
+
+  it('shows an error when loading books fails', async () => {
+    const fetchMock = vi.fn().mockResolvedValue({
+      ok: false,
+      json: async () => ({}),
+    });
+    vi.stubGlobal('fetch', fetchMock);
+    const { BookPickerModal } = await import('@/components/bookdate/BookPickerModal');
+
+    render(
+      <BookPickerModal
+        isOpen={true}
+        onClose={vi.fn()}
+        selectedIds={[]}
+        onConfirm={vi.fn()}
+        maxSelection={5}
+      />
+    );
+
+    expect(await screen.findByText('Failed to load library books')).toBeInTheDocument();
+  });
+
+  it('shows an empty search state when no books match', async () => {
+    const fetchMock = vi.fn().mockResolvedValue({
+      ok: true,
+      json: async () => ({ books }),
+    });
+    vi.stubGlobal('fetch', fetchMock);
+    const { BookPickerModal } = await import('@/components/bookdate/BookPickerModal');
+
+    render(
+      <BookPickerModal
+        isOpen={true}
+        onClose={vi.fn()}
+        selectedIds={[]}
+        onConfirm={vi.fn()}
+        maxSelection={5}
+      />
+    );
+
+    await screen.findByRole('button', { name: /First Book/ });
+
+    fireEvent.change(screen.getByPlaceholderText('Search books...'), { target: { value: 'missing' } });
+
+    expect(screen.getByText('No books match your search')).toBeInTheDocument();
+  });
+
+  it('clears selection and disables confirm', async () => {
+    const fetchMock = vi.fn().mockResolvedValue({
+      ok: true,
+      json: async () => ({ books }),
+    });
+    vi.stubGlobal('fetch', fetchMock);
+    const { BookPickerModal } = await import('@/components/bookdate/BookPickerModal');
+
+    render(
+      <BookPickerModal
+        isOpen={true}
+        onClose={vi.fn()}
+        selectedIds={['book-1']}
+        onConfirm={vi.fn()}
+        maxSelection={5}
+      />
+    );
+
+    await screen.findByRole('button', { name: /First Book/ });
+
+    const clearButton = screen.getByRole('button', { name: 'Clear Selection' });
+    fireEvent.click(clearButton);
+
+    expect(screen.getByRole('button', { name: /Confirm Selection/ })).toBeDisabled();
+  });
+});