fix: address review findings from PR #402 MEP systems

- core: fix layer violation in level-height.ts — extract sceneRegistry
  import, replace with optional WallBaseYResolver callback so core stays
  pure (no Three.js mesh state); viewer callers pass resolver, headless
  callers (MCP/tests) get deterministic node-data-only result

- core: generalise port-connectivity service from duct-only to all
  distribution families — match partners by distributionRole ('run' →
  endpoint stretch, 'fitting' → rigid follow) instead of hard-coded
  duct-segment/duct-fitting type names; add system-compat guard so
  cross-system ports (e.g. supply duct vs waste pipe) don't fuse

- editor: fix port-snap rotation bug in move tool — pass preview node
  at live rotation into resolvePortSnap so own-port positions reflect
  any mid-drag R/T rotation before computing the snap delta

- editor: wire pipe-trap into UI — add to StructureTool union,
  MepToolKind, MEP_ITEMS Build-tab tile, and structure-tools action menu

- test: add port-connectivity-pipe.test.ts — 2 tests covering
  pipe-fitting → pipe-segment endpoint drag and cross-system isolation

- test: fix stale pipe-auto-fitting.test.ts wye expectation — author
  deliberately chose square sanitary-tee for DWV side-taps (documented
  in PR description and PipeFittingNode schema); update the one test
  that still expected wye to match the implemented behaviour

- nit: fix optional-chain biome warning in validate-dwv.ts

packages/nodes/src/duct-segment/tool.tsx

@@ -6,6 +6,7 @@ import {
   emitter,
   type GridEvent,
   getLevelHeight,
+  sceneRegistry,
   useScene,
 } from '@pascal-app/core'
 import {
@@ -551,7 +552,9 @@ const DuctSegmentTool = () => {
     // ceiling (centerline = ceiling height − radius).
     const resolveBaseY = (): number => {
       if (!ceilingModeRef.current) return 0
-      const ceiling = getLevelHeight(activeLevelId, useScene.getState().nodes)
+      const ceiling = getLevelHeight(activeLevelId, useScene.getState().nodes, (wallId) =>
+        sceneRegistry.nodes.get(wallId)?.position.y,
+      )
       const p = profileRef.current
       const verticalIn = p.shape === 'round' ? p.diameter : p.height
       return Math.max(0, ceiling - (verticalIn * 0.0254) / 2)