Second PR in the Studio storyboarding stack. Adds the top-level toggle
between the storyboard and the timeline/preview stage, behind the flag.
- STUDIO_STORYBOARD_ENABLED flag (VITE_STUDIO_ENABLE_STORYBOARD, default
off) now gates the UI.
- ViewModeContext: timeline|storyboard state mirrored to the ?view= query
param, so it survives reloads and an agent can deep-link ?view=storyboard.
- Segmented Storyboard|Preview control in StudioHeader (flag-gated).
- StudioApp swaps the whole center stage for a full-width StoryboardView
when storyboard mode is active.
- useStoryboard hook + StoryboardView shell: global-direction header,
loading/error/empty states. The frame contact-sheet grid lands in PR3.
- Extract StudioOverlays from App.tsx to stay within the 600-line studio
decomposition budget.
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
