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/viewer/src/r3f.d.ts

@@ -0,0 +1,8 @@
+// Augment @react-three/fiber's ThreeElements to include all Three.js JSX intrinsic elements.
+// This must be a project-wide declaration so all files can use <directionalLight />, etc.
+import type { ThreeToJSXElements } from '@react-three/fiber'
+import * as THREE from 'three/webgpu'
+
+declare module '@react-three/fiber' {
+  interface ThreeElements extends ThreeToJSXElements<typeof THREE> {}
+}