feat: HVAC ductwork + DWV plumbing systems (#402)

Adds two new MEP node families (HVAC ductwork, DWV plumbing) built on a shared port-connectivity model. Co-authored by @sudhir9297.

packages/viewer/src/systems/level/level-system.tsx

@@ -1,8 +1,7 @@
-import { type LevelNode, sceneRegistry, useScene } from '@pascal-app/core'
+import { getLevelHeight, type LevelNode, sceneRegistry, useScene } from '@pascal-app/core'
 import { useFrame } from '@react-three/fiber'
 import { lerp } from 'three/src/math/MathUtils.js'
 import useViewer from '../../store/use-viewer'
-import { getLevelHeight } from './level-utils'
 
 const EXPLODED_GAP = 5