The 7th and last of the legacy interaction flags. The node being placed/moved
now lives inside the interaction scope's `placing`/`moving` variant (carried
inline, since fresh-placement/duplicate drafts aren't in the scene yet), read via
`useMovingNode()` / `getMovingNode()` / `movingNodeOf(scope)`.
- scope.ts: `placing`/`moving` carry `node: AnyNode`; add `movingNodeOf`.
- use-interaction-scope.ts: `useMovingNode` (hook) + `getMovingNode` (imperative);
no useRef snapshot needed — the node is set once at `begin`, stable for the gesture.
- use-editor.tsx: drop the `movingNode` field + the `set({ movingNode })` writes.
`setMovingNode` still drives the scope and still sets `movingNodeOrigin` /
`placementDragMode`, so cross-store subscribers keep firing. Param + ~90 call
sites unchanged.
- migrate ~17 reader sites to `useMovingNode()` / `getMovingNode()`; drop
`movingNode` from lib/scene.ts; export `movingNodeOf`.
Every interaction flag is now derived from the single authoritative scope; only
`movingNodeOrigin` + `placementDragMode` intentionally remain as useEditor flags
(they outlive the scope / gate companion behavior).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
