refactor(web): sweep 8 test files to use pageUrlModule() (#375)

Centralizes the inline { page: { get url() { return state.pageUrl } } }
mock shape via test-utils/mocks/appState.ts. The vi.hoisted state
declaration remains per-file (vitest mock-hoisting requires module-
level declaration). Adds a $test-utils alias to svelte.config.js so
the helper can be imported without ../../../ chains.

SKIPPED (mock exposes more than url):
- Shell.test.ts, MobileNavDrawer.test.ts, admin.test.ts: static
  page: { url: ... } shape, no hoisted state to centralize.
- album.test.ts, artist.test.ts: page exposes both params and url.
- playlist.test.ts, reset-password.test.ts: page exposes params only.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

web/src/routes/search/artists/artists.test.ts

@@ -1,28 +1,19 @@
 import { afterEach, describe, expect, test, vi } from 'vitest';
 import { render, screen, fireEvent } from '@testing-library/svelte';
-import { readable } from 'svelte/store';
 import { mockInfiniteQuery } from '../../../test-utils/query';
+import { emptyLikesMock } from '../../../test-utils/mocks/likes';
+import { pageUrlModule } from '$test-utils/mocks/appState';
 import type { ArtistRef, Page } from '$lib/api/types';
 
 const state = vi.hoisted(() => ({ pageUrl: new URL('http://localhost/search/artists?q=miles') }));
 
-vi.mock('$app/state', () => ({
-  page: { get url() { return state.pageUrl; } }
-}));
+vi.mock('$app/state', () => pageUrlModule(state));
 
 vi.mock('$lib/api/queries', () => ({
   createSearchArtistsInfiniteQuery: vi.fn()
 }));
 
-vi.mock('$lib/api/likes', () => ({
-  createLikedIdsQuery: () => readable({
-    data: { track_ids: [], album_ids: [], artist_ids: [] },
-    isPending: false,
-    isError: false
-  }),
-  likeEntity: vi.fn(),
-  unlikeEntity: vi.fn()
-}));
+vi.mock('$lib/api/likes', () => emptyLikesMock());
 
 import ArtistsOverflow from './+page.svelte';
 import { createSearchArtistsInfiniteQuery } from '$lib/api/queries';