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/spawn/renderer.tsx

@@ -1,6 +1,12 @@
 'use client'
 
-import { type SpawnNode, useLiveTransforms, useRegistry } from '@pascal-app/core'
+import {
+  type AnyNodeId,
+  type SpawnNode,
+  useLiveNodeOverrides,
+  useLiveTransforms,
+  useRegistry,
+} from '@pascal-app/core'
 import { createDefaultMaterial, useNodeEvents, useViewer } from '@pascal-app/viewer'
 import { useMemo, useRef } from 'react'
 import { Color, type Group, Shape } from 'three'
@@ -20,6 +26,11 @@ const SPAWN_COLOR = new Color('#22c55e')
 const SpawnRenderer = ({ node }: { node: SpawnNode }) => {
   const ref = useRef<Group>(null!)
   const handlers = useNodeEvents(node, 'spawn')
+  const liveOverride = useLiveNodeOverrides((state) => state.get(node.id as AnyNodeId))
+  const effectiveNode = useMemo(
+    () => (liveOverride ? ({ ...node, ...liveOverride } as SpawnNode) : node),
+    [node, liveOverride],
+  )
   const liveTransform = useLiveTransforms((state) => state.get(node.id))
   const walkthroughMode = useViewer((state) => state.walkthroughMode)
   const shading = useViewer((state) => state.shading)
@@ -52,10 +63,10 @@ const SpawnRenderer = ({ node }: { node: SpawnNode }) => {
 
   return (
     <group
-      position={liveTransform?.position ?? node.position}
+      position={liveTransform?.position ?? effectiveNode.position}
       ref={ref}
-      rotation={[0, liveTransform?.rotation ?? node.rotation, 0]}
-      visible={!walkthroughMode}
+      rotation={[0, liveTransform?.rotation ?? effectiveNode.rotation, 0]}
+      visible={!walkthroughMode && effectiveNode.visible !== false}
     >
       <mesh position={[0, 0.09, 0]} rotation={[-Math.PI / 2, 0, 0]} {...handlers}>
         <ringGeometry args={[0.34, 0.48, 48]} />