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/ui/StickyPagination.test.tsx

@@ -0,0 +1,133 @@
+/**
+ * Component: Sticky Pagination Tests
+ * Documentation: documentation/frontend/components.md
+ */
+
+// @vitest-environment jsdom
+
+import React from 'react';
+import { act, fireEvent, render, screen } from '@testing-library/react';
+import { beforeEach, describe, expect, it, vi } from 'vitest';
+import { StickyPagination } from '@/components/ui/StickyPagination';
+
+type ObserverEntry = {
+  isIntersecting: boolean;
+  intersectionRatio: number;
+  target: Element;
+};
+
+describe('StickyPagination', () => {
+  const observers: { callback: IntersectionObserverCallback }[] = [];
+
+  beforeEach(() => {
+    observers.length = 0;
+    class MockIntersectionObserver {
+      callback: IntersectionObserverCallback;
+      observe = vi.fn();
+      unobserve = vi.fn();
+      disconnect = vi.fn();
+      takeRecords = vi.fn();
+
+      constructor(callback: IntersectionObserverCallback) {
+        this.callback = callback;
+        observers.push(this);
+      }
+    }
+
+    (global as any).IntersectionObserver = MockIntersectionObserver;
+  });
+
+  it('returns null when there is only one page', () => {
+    const sectionRef = { current: document.createElement('div') };
+    const { container } = render(
+      <StickyPagination
+        currentPage={1}
+        totalPages={1}
+        onPageChange={vi.fn()}
+        sectionRef={sectionRef}
+        label="Popular"
+      />
+    );
+
+    expect(container.firstChild).toBeNull();
+  });
+
+  it('shows and hides based on section and footer visibility', () => {
+    const sectionRef = { current: document.createElement('div') };
+    const footerRef = { current: document.createElement('div') };
+
+    const { container } = render(
+      <StickyPagination
+        currentPage={2}
+        totalPages={5}
+        onPageChange={vi.fn()}
+        sectionRef={sectionRef}
+        footerRef={footerRef}
+        label="Popular"
+      />
+    );
+
+    const root = container.querySelector('div.fixed') as HTMLElement;
+    expect(root).toHaveClass('opacity-0');
+
+    act(() => {
+      observers[0].callback(
+        [
+          {
+            isIntersecting: true,
+            intersectionRatio: 0.2,
+            target: sectionRef.current as Element,
+          } as ObserverEntry,
+        ],
+        observers[0] as unknown as IntersectionObserver
+      );
+    });
+
+    expect(root).toHaveClass('opacity-100');
+
+    act(() => {
+      observers[1].callback(
+        [
+          {
+            isIntersecting: true,
+            intersectionRatio: 0.2,
+            target: footerRef.current as Element,
+          } as ObserverEntry,
+        ],
+        observers[1] as unknown as IntersectionObserver
+      );
+    });
+
+    expect(root).toHaveClass('opacity-0');
+  });
+
+  it('handles navigation and jump input updates', () => {
+    const sectionRef = { current: document.createElement('div') };
+    const onPageChange = vi.fn();
+
+    render(
+      <StickyPagination
+        currentPage={2}
+        totalPages={4}
+        onPageChange={onPageChange}
+        sectionRef={sectionRef}
+        label="Popular"
+      />
+    );
+
+    fireEvent.click(screen.getByLabelText('Next page'));
+    expect(onPageChange).toHaveBeenCalledWith(3);
+
+    fireEvent.click(screen.getByLabelText('Previous page'));
+    expect(onPageChange).toHaveBeenCalledWith(1);
+
+    const input = screen.getByLabelText('Current page') as HTMLInputElement;
+    fireEvent.change(input, { target: { value: '4' } });
+    fireEvent.blur(input);
+    expect(onPageChange).toHaveBeenCalledWith(4);
+
+    fireEvent.change(input, { target: { value: '99' } });
+    fireEvent.blur(input);
+    expect(input.value).toBe('2');
+  });
+});