Consolidate the Race Story section into a cohesive timeline surface: custom
chapter-strip scrolling with active-card sync, unified segmented playback
controls, chapter bands on the position graph with decimated axes and
de-collided labels, map toggle gated by an on-mount replay/outline probe,
and shared empty-state cards. Adds vitest coverage and visual snapshots.
Note: replay/outline queries now probe on mount (not only when Map opens) so
the toggle can be hidden before users hit a dead panel.
Co-authored-by: Cursor <cursoragent@cursor.com>
