Return whether an older installed version should warn about updating.
True only when a fresh cache says an update is available and the installed
version's release is at least INSTALLED_STALE_NOTICE_DAYS old. Returns
False for editable/dev installs (release age is meaningless there), when
update checks are disabled (the opt-out silences this too), and when the age
or update answer is unknown.
Best-effort: any unexpected error degrades to False rather than
propagating, so this cosmetic check can never abort TUI startup.
