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/viewer/index.tsx

@@ -11,7 +11,6 @@ import { FenceSystem } from '../../systems/fence/fence-system'
 import { GuideSystem } from '../../systems/guide/guide-system'
 import { ItemSystem } from '../../systems/item/item-system'
 import { ItemLightSystem } from '../../systems/item-light/item-light-system'
-import { ItemMeshMetadataSystem } from '../../systems/item-mesh-metadata/item-mesh-metadata-system'
 import { LevelSystem } from '../../systems/level/level-system'
 import { RoofSystem } from '../../systems/roof/roof-system'
 import { ScanSystem } from '../../systems/scan/scan-system'
@@ -239,7 +238,6 @@ const Viewer: React.FC<ViewerProps> = ({
         {/* <DebugRenderer /> */}
 
         <ItemLightSystem />
-        <ItemMeshMetadataSystem />
         {selectionManager === 'default' && <SelectionManager />}
         {perf && <PerfMonitor />}
         {children}