Function spawn_startup_check 

pub fn spawn_startup_check(app: AppHandle, settings: &Settings)

Opt-in startup auto-check (the auto_check_updates setting). Checks the updater endpoint once in the background and posts a non-intrusive desktop notification if a newer build is available. Silent on no-update and on any error — being offline must never nag — and never blocks startup. Split on cfg(test) (mirrors overlay::spawn_render_watchdog) so the test/coverage build neither spawns a task nor fires a real OS notification; the decision logic lives in the pure, tested update_notification.