CI failed with an unhandled `ReferenceError: window is not defined` thrown from
a Mantine `Transition` `setTimeout` (`use-transition.mjs`) firing after the test
environment was torn down — every test passed, but the leaked timer failed the
run. happy-dom has no `matchMedia`, so `useReducedMotion` resolves to
"motion allowed" and every Transition (ScreenStage, Modal, …) schedules real
enter/exit timers; a timer that outlives its test throws post-teardown. This
surfaced now because MonitoringScreen started wrapping its screens in
ScreenStage (a Transition) where it previously rendered them directly.
Mock `window.matchMedia` in the test setup to report
`prefers-reduced-motion: reduce`, so Mantine transitions render instantly (no
timers). All other queries return `false`, matching the prior absent-matchMedia
behavior, so `useMediaQuery`-driven layout is unchanged. Full unit suite passes
with no unhandled errors across repeated runs.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BrihGWcrM9JGRyu41nzZYw
1e6718e2fd