Closes the spawn-time half of the replay-overlay redesign open in
SESSION_HANDOFF.md by adding the 1px cyan scrub bar called for in
docs/ui-mockups/replay-overlay-mobile.html. A track in BORDER_SUBTLE
spans the bottom edge of the banner and the cyan ACCENT_PRIMARY fill
mirrors cursor / total via a new ReplayOverlayScrubFill component +
update_scrub_fill system. The pure scrub_pct helper is shared between
the spawn path (initial fill width) and the per-frame updater so the
first paint already reflects state instead of popping 0 → cursor on
the first tick — same shape as the existing format_progress /
update_progress_text split.
Two new tests (1176 → 1178): scrub_pct_covers_state_corners pins the
helper's four corners (Inactive / cursor=0 / midpoint / Completed) and
overlay_scrub_fill_tracks_cursor drives ReplayPlaybackState end-to-end
and asserts Node.width on the unique scrub-fill entity. Same change-
detection guard as the text updaters, so an idle replay leaves the
node untouched.
Header text treatment, move-log scroll, MOVE chip, and WIN MOVE callout
from the same mockup are still open — separate commits.
funman300
c84d9f445c