feat(editor): unify placement/move facing triangle into one editor-side renderer

Every placement and move path now publishes its ghost pose to a single
`useFacingPose` store, drawn by one editor-side `<FacingPoseIndicator>` overlay,
instead of each path drawing its own triangle (which left the nodes-package and
PlacementBox paths invisible):

- column/shelf presets + all moves (PlacementBox via move-registry, and
  DragBoundingBox) now publish the pose, so the triangle finally shows
- stair create + move use a declarative `facingIndicator: { reversed: true }`
  (new registry resolver) so the triangle sits before the entry pointing out —
  resolved in one place, so create and move match automatically
- stair placement defaults to single and respects the shared `point`
  continuation (C) toggle, like the other placement tools

Checkpoint on the placement-interaction epic: also carries the in-flight
continuation-profile extraction (lib/continuation), grid surface (item #8), and
HUD work. Door/window still render their own legacy inline triangle and are
migrated to the overlay next.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

packages/nodes/src/item/definition.ts

@@ -167,6 +167,7 @@ function itemWallMoveHandle(): HandleDescriptor<ItemNodeType> {
 export const itemDefinition: NodeDefinition<typeof ItemNode> = {
   kind: 'item',
   snapProfile: 'item',
+  facingIndicator: true,
   schemaVersion: 1,
   schema: ItemNode,
   category: 'furnish',

packages/nodes/src/item/tool.tsx

@@ -35,10 +35,7 @@ function ItemPlacementContent({ selectedItem }: { selectedItem: AssetInput }) {
     },
     onCommitted: () => {
       triggerSFX('sfx:item-place')
-      // Returning `true` tells the coordinator to immediately spawn the
-      // next draft so the user can keep placing copies — matches the
-      // "repeat-on-click" UX of the legacy tool.
-      return true
+      return useEditor.getState().getContinuation('point') === 'repeat'
     },
   })