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/routes/login/login.test.ts

@@ -1,6 +1,6 @@
 import { afterEach, describe, expect, test, vi } from 'vitest';
 import { render, screen, fireEvent, waitFor } from '@testing-library/svelte';
-import { pageUrlModule } from '$test-utils/mocks/appState';
+import { pageUrlModule } from '#test-utils/mocks/appState.js';
 
 // vi.hoisted avoids the temporal-dead-zone hazard: mock factories are lazy
 // and can run before top-level `let` is initialized, since imports are