fix(studio): drop dead keyframe menu wiring and close the R1 review items

The diamond context menu still declared `onChangeEase` and `onCopyProperties`
props, and `TimelineOverlays` still threaded `onChangeKeyframeEase` plus a
`keyframeCache` it never read. Nothing on any timeline branch calls them, so
they are removed along with the `onChangeKeyframeEase` callback implementation.

Also from review:
- `deleteSelectedKeyframes` only falls back to the sole keyframed animation when
  there is exactly one. A collapsed selection key carries no animation id, so
  taking the first of several deleted an arbitrary tween's keyframe.
- The duration-less retime test asserts the real 87.601% instead of
  `expect.any(Number)`, so a wrong timing basis fails it.
- `Timeline` wires the keyframe handlers' `onSelectSegment` through to the
  diamonds; it was built and then dropped, so segment ease selection never fired.
- The flat text section arms auto-focus in state rather than reading and
  clearing a ref during render, which Strict Mode's double render swallowed.

packages/studio/src/player/components/timelineCallbacks.ts

@@ -74,7 +74,6 @@ export interface TimelineEditCallbacks {
   onRazorSplitAll?: (splitTime: number) => Promise<void> | void;
   onDeleteKeyframe?: (elementId: string, keyframe: TimelineKeyframeTarget) => void;
   onDeleteAllKeyframes?: (element: TimelineElement) => void;
-  onChangeKeyframeEase?: (elementId: string, percentage: number, ease: string) => void;
   onMoveKeyframeToPlayhead?: (element: TimelineElement, keyframe: TimelineKeyframeTarget) => void;
   /** Drag-to-retime: `keyframe` identifies the dragged keyframe (its percentage
    *  is clip-relative), `toClipPercentage` is the neighbour-clamped drop. */