feat(editor): precise item dimensions — static bounding boxes, placement-math, remove item-mesh-metadata system

- Replace runtime mesh-based bounding-box computation with static dimension-based polygons for item footprints
- Add snapUpToGridStep() and getGridAlignedDimensions() to placement-math for grid-cell-aligned placement wireframes
- Add expandBoundsToGrid() to use-placement-coordinator for consistent wireframe snapping
- Add currentCursorRotationY to PlacementContext; preserve world orientation across item-surface transitions
- Fix item detach from surface: use worldToBuildingLocal() instead of event.localPosition to avoid coordinate-space jump
- Subscribe to useLiveTransforms in FloorplanPanel during placement so R/T keyboard rotation refreshes the 2D overlay immediately
- Fix FloorplanItemImage rotation (+180° to account for top-down camera capture orientation)
- Simplify spatial-grid-manager: single dimension-based getItemLocalBounds(), removes runtime mesh-metadata path
- Remove item-mesh-metadata system (compute-item-mesh-metadata, item-mesh-metadata-system, sync-request)

packages/viewer/src/components/renderers/item/item-renderer.tsx

@@ -21,10 +21,6 @@ import { useNodeEvents } from '../../../hooks/use-node-events'
 import { resolveCdnUrl } from '../../../lib/asset-url'
 import { baseMaterial, glassMaterial } from '../../../lib/materials'
 import { useItemLightPool } from '../../../store/use-item-light-pool'
-import {
-  requestItemMeshMetadataSync,
-  setItemMeshMetadataSourceRoot,
-} from '../../../systems/item-mesh-metadata/sync-request'
 import { ErrorBoundary } from '../../error-boundary'
 import { NodeRenderer } from '../node-renderer'
 
@@ -110,19 +106,6 @@ const ModelRenderer = ({ node }: { node: ItemNode }) => {
     useScene.getState().dirtyNodes.add(node.parentId as AnyNodeId)
   }, [node.parentId])
 
-  // Re-sync when GLTF `scene` or external `metadata` edits should invalidate cached footprint/bounds.
-  // biome-ignore lint/correctness/useExhaustiveDependencies: intentional — asset load and metadata drive mesh-metadata sync
-  useEffect(() => {
-    const cloneRoot = ref.current
-    if (!cloneRoot) return
-
-    setItemMeshMetadataSourceRoot(node.id, cloneRoot)
-    requestItemMeshMetadataSync(node.id)
-    return () => {
-      setItemMeshMetadataSourceRoot(node.id, null)
-    }
-  }, [node.id, node.metadata, scene])
-
   useEffect(() => {
     const interactive = interactiveRef.current
     if (!interactive) return