feat(studio): slideshow branching editor panel (#1582)

New Slideshow right-panel tab — slide list, inspector (notes + fragment
hold-points), branch tree, hotspot tool — backed by pure manifest-transform
helpers and a debounced SDK persist that writes the JSON island.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/studio/src/App.tsx

@@ -566,6 +566,10 @@ export function StudioApp() {
                         onToggleRecording={
                           STUDIO_KEYFRAMES_ENABLED ? handleToggleRecording : undefined
                         }
+                        sdkSession={sdkHandle.session}
+                        reloadPreview={reloadPreview}
+                        domEditSaveTimestampRef={domEditSaveTimestampRef}
+                        recordEdit={editHistory.recordEdit}
                       />
                     )}
                   </div>