feat: add narrative chapter headlines and race-hub chapter strip (#21)

Generate deterministic template headlines server-side for each replay chapter
kind, expose Chapter.headline in the race-hub payload, and render a horizontal
chapter strip on the story view with active-chapter highlighting, click-to-jump,
and a 90-second tour mode built on the existing scrubber playback.

Co-authored-by: Cursor <cursoragent@cursor.com>

internal/query/racehub.go

@@ -252,10 +252,38 @@ func (s *Service) GetRaceHub(sessionKey int) (RaceHub, error) {
 	}
 
 	hub.Chapters = chapters.Detect(hub.RaceControl, hub.Positions, hub.Laps, totalLaps(hub.Results, hub.Laps))
+	hub.Chapters = chapters.ApplyHeadlines(
+		hub.Chapters,
+		chapters.BuildDriverMap(hub.Drivers, driverIdentityInputs(hub.Results)),
+		hub.RaceControl,
+		winnerDriverNumber(hub.Results),
+	)
 	hub.Source = responseSource(hub.Datasets)
 	return hub, nil
 }
 
+func driverIdentityInputs(results []EnrichedResult) []chapters.DriverIdentityInput {
+	out := make([]chapters.DriverIdentityInput, 0, len(results))
+	for _, r := range results {
+		out = append(out, chapters.DriverIdentityInput{
+			DriverNumber: r.DriverNumber,
+			NameAcronym:  r.NameAcronym,
+			FullName:     r.FullName,
+			TeamName:     r.TeamName,
+		})
+	}
+	return out
+}
+
+func winnerDriverNumber(results []EnrichedResult) int {
+	for _, r := range results {
+		if r.Position == 1 {
+			return r.DriverNumber
+		}
+	}
+	return 0
+}
+
 func totalLaps(results []EnrichedResult, laps []models.Lap) int {
 	total := 0
 	for _, result := range results {