fix(studio): remove keyframe dragging from the timeline (#1763)

Dragging timeline keyframe diamonds was unreliable — clip<->tween percentage
remapping, an optimistic-hold workaround, and an intermittent no-op/revert when
the GSAP session lagged the drag (its own comments document the flakiness). Remove
the drag interaction entirely: diamonds still display, click-to-seek, and offer the
context menu (add/remove/ease) — keyframe timing is edited via the playhead + panel,
which are deterministic. Deletes the keyframe-move plan module + its wiring through
TimelineClipDiamonds -> TimelineCanvas -> Timeline -> TimelineEditContext.

packages/studio/src/contexts/TimelineEditContext.tsx

@@ -39,7 +39,6 @@ export function TimelineEditProvider({
       value.onDeleteKeyframe,
       value.onDeleteAllKeyframes,
       value.onChangeKeyframeEase,
-      value.onMoveKeyframe,
       value.onToggleKeyframeAtPlayhead,
     ],
   );