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/api/auth-misc.routes.test.ts

@@ -95,6 +95,50 @@ describe('Auth misc routes', () => {
     expect(payload.accessToken).toBe('access-token');
   });
 
+  it('returns 400 when refresh token is missing', async () => {
+    const { POST } = await import('@/app/api/auth/refresh/route');
+    const response = await POST({ json: vi.fn().mockResolvedValue({}) } as any);
+    const payload = await response.json();
+
+    expect(response.status).toBe(400);
+    expect(payload.error).toBe('ValidationError');
+  });
+
+  it('returns 401 when refresh token is invalid', async () => {
+    verifyRefreshTokenMock.mockReturnValue(null);
+    const { POST } = await import('@/app/api/auth/refresh/route');
+    const response = await POST({ json: vi.fn().mockResolvedValue({ refreshToken: 'bad' }) } as any);
+    const payload = await response.json();
+
+    expect(response.status).toBe(401);
+    expect(payload.error).toBe('Unauthorized');
+  });
+
+  it('returns 401 when user is not found for refresh token', async () => {
+    verifyRefreshTokenMock.mockReturnValue({ sub: 'user-missing' });
+    prismaMock.user.findUnique.mockResolvedValue(null);
+
+    const { POST } = await import('@/app/api/auth/refresh/route');
+    const response = await POST({ json: vi.fn().mockResolvedValue({ refreshToken: 'refresh' }) } as any);
+    const payload = await response.json();
+
+    expect(response.status).toBe(401);
+    expect(payload.error).toBe('Unauthorized');
+  });
+
+  it('returns 500 when refresh token verification throws', async () => {
+    verifyRefreshTokenMock.mockImplementation(() => {
+      throw new Error('bad token');
+    });
+
+    const { POST } = await import('@/app/api/auth/refresh/route');
+    const response = await POST({ json: vi.fn().mockResolvedValue({ refreshToken: 'refresh' }) } as any);
+    const payload = await response.json();
+
+    expect(response.status).toBe(500);
+    expect(payload.error).toBe('RefreshError');
+  });
+
   it('returns provider info for audiobookshelf mode', async () => {
     configServiceMock.get
       .mockResolvedValueOnce('audiobookshelf')