3 code paths in desktop.smoke.spec.ts used bare `return` when fixtures
were unavailable (runtime not configured, too few model toggles), which
caused the test to silently pass without exercising the real flow.
Replace with `test.skip(true, reason)` so Playwright reports the skip
and surfaces the missing precondition.
- Add second test to desktop.smoke.spec.ts validating app launch, window dimensions, and screenshot capture
- Screenshot saved to build/screenshots/launch-{platform}.png for D-07 evidence
- Update playwright.config.ts with outputDir for test artifacts and join import
- Add xvfb-run note for headless Linux CI environments
ZacharyZhang-NY