Migrate the two pure-mirror interaction flags off `useEditor` onto the
authoritative `useInteractionScope`. Both carried payloads byte-identical to
the scope union, so this is a zero-behaviour-change refactor: readers use the
reference-stable `useEditingHole()` / `useActiveHandleDrag()` hooks (or the
`getEditingHole()` imperative read), and producers drive the scope directly
with guarded `endIf` so clearing one interaction never stomps an unrelated
scope. Adds the `holeEditScope` builder + a no-leaked-flag invariant test.
Closes the first slice of the legacy-flag deletion; the rich-payload flags
(movingNode, curving*, *Endpoint, placementDragMode) remain.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
