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/column/definition.ts

@@ -315,6 +315,7 @@ function columnHandles(node: ColumnNodeType): HandleDescriptor<ColumnNodeType>[]
 export const columnDefinition: NodeDefinition<typeof ColumnNode> = {
   kind: 'column',
   snapProfile: 'item',
+  facingIndicator: true,
   schemaVersion: 1,
   schema: ColumnNode,
   category: 'structure',

packages/nodes/src/column/tool.tsx

@@ -16,6 +16,7 @@ import {
   triggerSFX,
   useAlignmentGuides,
   useEditor,
+  useFacingPose,
   usePlacementPreview,
 } from '@pascal-app/editor'
 import { useViewer } from '@pascal-app/viewer'
@@ -101,6 +102,13 @@ const ColumnTool = () => {
         levelId: activeLevelId,
       })
       cursorRef.current?.position.set(...visualPosition)
+      // Forward-facing floor triangle, drawn by the editor-side overlay. Columns
+      // never rotate (`rotation: 0`), so the triangle just sits in front.
+      useFacingPose.getState().set({
+        position: visualPosition,
+        rotationY: previewNode.rotation,
+        depth: previewNode.depth,
+      })
       lastCursorRef.current = position
 
       // Publish a transient, positioned preview node for the 2D floor-plan
@@ -130,12 +138,17 @@ const ColumnTool = () => {
       useScene.getState().createNode(column, activeLevelId)
       useViewer.getState().setSelection({ selectedIds: [column.id] })
       triggerSFX('sfx:structure-build')
-      // The placed column is now a valid alignment target for the next one;
-      // refresh the candidate pool and drop the guide from this drop. The
-      // 2D ghost re-publishes on the next move.
-      alignmentCandidates = collectAlignmentAnchors(useScene.getState().nodes, previewNode.id)
       useAlignmentGuides.getState().clear()
       usePlacementPreview.getState().clear()
+      if (useEditor.getState().getContinuation('point') === 'repeat') {
+        // The placed column is now a valid alignment target for the next one.
+        alignmentCandidates = collectAlignmentAnchors(useScene.getState().nodes, previewNode.id)
+      } else {
+        cursorVisibleRef.current = false
+        setCursorVisible(false)
+        useFacingPose.getState().clear()
+        useEditor.getState().setTool(null)
+      }
       stopPlacementCommitPropagation(event)
     }
 
@@ -147,6 +160,7 @@ const ColumnTool = () => {
       unsubscribePlacementClicks()
       useAlignmentGuides.getState().clear()
       usePlacementPreview.getState().clear()
+      useFacingPose.getState().clear()
     }
   }, [activeLevelId, previewNode])