Mock getBaseUrl in Audible service tests

Add a getBaseUrl mock to audibleServiceMock in audiobooks-browse route tests that returns 'https://www.audible.com'. This ensures tests have a defined base URL for Audible service calls and prevents issues caused by an undefined method during test execution.

tests/api/audiobooks-browse.routes.test.ts

@@ -10,6 +10,7 @@ const prismaMock = createPrismaMock();
 const audibleServiceMock = vi.hoisted(() => ({
   search: vi.fn(),
   getAudiobookDetails: vi.fn(),
+  getBaseUrl: vi.fn().mockReturnValue('https://www.audible.com'),
 }));
 const enrichMock = vi.hoisted(() => vi.fn());
 const currentUserMock = vi.hoisted(() => vi.fn());