- MenuBar: hover another title with a menu open to switch (scrubbing)
- menu popup width computed from the longest label; ROW_HEIGHT 22
- dock tab bar 26px / smaller tab text; viewer transport tightened
W5 timeline supplements: clicking a track header toggles the track in a
selected_tracks set and emits TimelineEvent::TrackSelected; clips with in/out
transitions get a resize handle at the wedge edge that emits
TimelineEvent::TransitionChanged with the clamped new length (delta-scaled
by zoom). Both follow the request-only contract. 182 gpui tests pass.