chore(web): clear kit 3's alias and Vite's config-loader deprecations (#5021)

CI run 8789 warned on both:

- kit 3 deprecates `config.alias`. The $test-utils alias becomes a
  `#test-utils/*` subpath import, matching #lib, and its 43 import sites
  move with it.
- Vite's coming native config loader needs the extension on
  vitest.config.ts's import of vite.config.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/src/lib/player/events.svelte.test.ts

@@ -21,7 +21,7 @@ import {
 } from './store.svelte';
 import { api } from '#lib/api/client.js';
 import type { TrackRef } from '#lib/api/types.js';
-import { makeTrack } from '$test-utils/fixtures/track';
+import { makeTrack } from '#test-utils/fixtures/track.js';
 
 function track(id: string, dur = 200): TrackRef {
   return makeTrack({

web/src/lib/player/gain.test.ts

@@ -2,7 +2,7 @@ import { describe, expect, test } from 'vitest';
 import { dbToLinear, gainDb, playingAsAlbum, MAX_BOOST_DB } from './gain';
 import type { NormalizationPrefs } from '#lib/api/normalization.js';
 import type { TrackRef } from '#lib/api/types.js';
-import { makeTrack } from '$test-utils/fixtures/track';
+import { makeTrack } from '#test-utils/fixtures/track.js';
 
 const prefs = (over: Partial<NormalizationPrefs> = {}): NormalizationPrefs => ({
   mode: 'auto',

web/src/lib/player/gainStage.svelte.test.ts

@@ -1,6 +1,6 @@
 import { beforeEach, describe, expect, test, vi } from 'vitest';
 import type { TrackRef } from '#lib/api/types.js';
-import { makeTrack } from '$test-utils/fixtures/track';
+import { makeTrack } from '#test-utils/fixtures/track.js';
 
 vi.mock('#lib/auth/store.svelte.js', () => ({
   user: {

web/src/lib/player/mediaSession.svelte.test.ts

@@ -1,7 +1,7 @@
 import { afterEach, beforeEach, describe, expect, test, vi } from 'vitest';
 import { flushSync } from 'svelte';
 import type { TrackRef } from '#lib/api/types.js';
-import { makeTrack } from '$test-utils/fixtures/track';
+import { makeTrack } from '#test-utils/fixtures/track.js';
 
 function track(id: string): TrackRef {
   return makeTrack({

web/src/lib/player/persisted.test.ts

@@ -1,6 +1,6 @@
 import { describe, it, expect, beforeEach, afterEach, vi } from 'vitest';
 import { readPersistedQueue, writePersistedQueue, clearPersistedQueue } from './persisted';
-import { makeTrack } from '$test-utils/fixtures/track';
+import { makeTrack } from '#test-utils/fixtures/track.js';
 
 const sampleTrack = makeTrack();
 

web/src/lib/player/shortcuts.svelte.test.ts

@@ -1,7 +1,7 @@
 import { afterEach, beforeEach, describe, expect, test } from 'vitest';
 import { flushSync } from 'svelte';
 import type { TrackRef } from '#lib/api/types.js';
-import { makeTrack } from '$test-utils/fixtures/track';
+import { makeTrack } from '#test-utils/fixtures/track.js';
 
 function track(id: string): TrackRef {
   return makeTrack({

web/src/lib/player/store.test.ts

@@ -19,7 +19,7 @@ import {
 } from './store.svelte';
 import type { TrackRef } from '#lib/api/types.js';
 import { writePersistedQueue, clearPersistedQueue } from './persisted';
-import { makeTrack } from '$test-utils/fixtures/track';
+import { makeTrack } from '#test-utils/fixtures/track.js';
 
 vi.mock('#lib/auth/store.svelte.js', () => ({
   user: {