feat(editor): live floor-stacking, unified handle system, slab-hole editing + interaction polish (#375)

- Live slab-stacking Y previews for all floor-placed kinds (item/shelf/spawn/column/stair) during placement + both move pathways, via a shared core resolver; canonical positions unchanged.
- Unified 3D handle system (one drag pipeline + one visual primitive) with forgiving invisible hit-areas on every handle, kept on EDITOR_LAYER so they don't poison the MRT scene pass.
- Hover + click-to-edit slab holes in 3D (manual hole -> hole editor; stair/elevator hole -> select owner); generic cross-arrow polygon-move grip; normalized handle interaction colors.
- NaN-safe node mutations + non-finite shadow-light bounds guard.
- Built on #373 (level-scoped alignment / registry slab tool); #373 owns X/Z alignment, this owns Y floor-stacking.

packages/nodes/src/shelf/geometry.ts

@@ -7,6 +7,7 @@ import {
   type RenderShading,
 } from '@pascal-app/viewer'
 import { BoxGeometry, FrontSide, Group, type Material, Mesh } from 'three'
+import { sanitizeShelfDimensions } from './dimensions'
 import type { ShelfNode } from './schema'
 
 /**
@@ -69,10 +70,11 @@ function getShelfMaterial(node: ShelfNode, shading: RenderShading): Material {
 }
 
 export function buildShelfGeometry(
-  node: ShelfNode,
+  rawNode: ShelfNode,
   _ctx?: unknown,
   shading: RenderShading = 'rendered',
 ): Group {
+  const node = sanitizeShelfDimensions(rawNode)
   const group = new Group()
   group.name = 'shelf-geometry'
 
@@ -343,8 +345,9 @@ function addCornerPosts(
  * can host in the lowest cell.
  */
 export function shelfRowSurfaceYs(node: ShelfNode): number[] {
-  const ys = boardCenterYs(node).map((y) => y + node.thickness / 2)
-  const bottomApplies = node.style === 'cubby' || node.style === 'bookshelf'
-  if (node.withBottom && bottomApplies) ys.unshift(node.thickness)
+  const safe = sanitizeShelfDimensions(node)
+  const ys = boardCenterYs(safe).map((y) => y + safe.thickness / 2)
+  const bottomApplies = safe.style === 'cubby' || safe.style === 'bookshelf'
+  if (safe.withBottom && bottomApplies) ys.unshift(safe.thickness)
   return ys
 }