T09b overlays: lightbox, spotlight and tour, floating toolbar, peek; images fill their box; overlays take focus back when its element leaves the tree

tasks/ch31-43.md

@@ -167,7 +167,7 @@
 ## T37 Onboarding & Help — `src/onboarding`
 
 - [ ] OnboardingWizard
-- [ ] WelcomeTour → `overlays::Tour` (T09)
+- [ ] WelcomeTour → `overlays::Tour` (T09b)
 - [ ] Coachmark / Hotspot — Coachmark → `overlays::Spotlight`; Hotspot here
 - [ ] FeatureHighlight / NewBadge
 - [ ] Checklist (first-run tasks)