sync: update core and viewer from monorepo (#143)

Major changes:
- Roof system rewrite with roof-segment support
- Scene store refactor
- Spatial grid improvements
- Item light system
- Post-processing and selection manager updates
- Perf monitor component

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/core/src/lib/space-detection.ts

@@ -42,7 +42,7 @@ export function initSpaceDetectionSync(
         if (!currentWallsByLevel.has(levelId)) {
           currentWallsByLevel.set(levelId, new Set())
         }
-        currentWallsByLevel.get(levelId)!.add((node as any).id)
+        currentWallsByLevel.get(levelId)?.add((node as any).id)
       }
     }