build(test): run unit tests with vitest and jsdom

Karma needed headless Chrome. Vitest with jsdom runs with no browser.
Lighthouse CI now gets Chrome from @puppeteer/browsers.
Two CSS font tests are dropped: jsdom does not apply real CSS.

GEMINI.md

@@ -39,6 +39,7 @@ To run the unit tests:
 ```bash
 ng test
 ```
+`npm test` runs once (Vitest + jsdom). `ng test` watches in a terminal; use `--watch=false` to run once.
 
 ### Linting