refactor(web): sweep 24 test files to use makeTrack/makeTracks fixtures (#375)

Replaces inline TrackRef literal redefinitions with calls to the
test-utils helper. Tests that asserted on default field values
(e.g. track titles, artist names rendered in the DOM) keep explicit
overrides; tests that only need a stub for shape now use makeTrack()
with no overrides.

PlaylistCard.test.ts, PlaylistTrackRow.test.ts, and playlist.test.ts
SKIPPED — they use PlaylistTrack (with track_id/added_at), not TrackRef.
ArtistCard.svelte and +page.svelte route files (matched by initial grep)
SKIPPED — live code, not test files.

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

web/src/lib/utils/dayGroup.test.ts

@@ -1,20 +1,11 @@
 import { describe, it, expect } from 'vitest';
 import { dayBucket, groupByDay } from './dayGroup';
 import type { HistoryEvent } from '$lib/api/history';
-import type { TrackRef } from '$lib/api/types';
+import { makeTrack } from '$test-utils/fixtures/track';
 
 const NOW = new Date('2026-05-04T14:00:00Z');
 
-const stubTrack: TrackRef = {
-  id: 'track-x',
-  title: 'Song X',
-  album_id: 'al-x',
-  album_title: 'Album X',
-  artist_id: 'ar-x',
-  artist_name: 'Artist X',
-  duration_sec: 200,
-  stream_url: '/stream/x'
-};
+const stubTrack = makeTrack();
 
 const mkEvent = (id: string, playedAt: string): HistoryEvent => ({
   id,