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/vite.config.ts

@@ -57,7 +57,7 @@ const injectGoTokensPlugin = {
 };
 
 // SvelteKit's options, which lived in svelte.config.js before kit 3. Exported
-// so vitest.config.ts runs the same kit setup (the $test-utils alias above all).
+// so vitest.config.ts runs the same kit setup.
 export const kitOptions = {
   preprocess: vitePreprocess(),
   adapter: adapter({
@@ -67,13 +67,7 @@ export const kitOptions = {
     precompress: false,
     strict: false
   }),
-  files: { assets: 'static' },
-  alias: {
-    // test-only helper barrel; resolves the same way #lib does so test
-    // files can import shared mock factories without ../../../ chains.
-    '$test-utils': 'src/test-utils',
-    '$test-utils/*': 'src/test-utils/*'
-  }
+  files: { assets: 'static' }
 };
 
 export default defineConfig({