fix: address 2nd-round adversarial review of PR #402 fixes

- core: decouple drag-follow from distributionRole — add
  portConnectivityFollow flag to NodeDefinition; pipe-trap opts out
  (portConnectivityFollow: false) so dragging a connected pipe endpoint
  stretches the trap arm instead of yanking the anchored trap fixture

- core: remove the module-level getLevelHeight cache entirely — it was
  keyed only by nodes-object identity, which could return stale heights
  for in-place mutations by pure/headless callers. The function is now
  fully pure and deterministic; viewer hot path recomputes per frame as
  before (the cache only ever skipped the resolver-free branch)

- test: harden port-connectivity-pipe.test.ts — real DuctSegmentNode
  cross-family isolation case (was waste-vs-vent), new pipe-trap anchor
  case (run drag doesn't move trap; trap drag still stretches run), and
  beforeEach/afterEach registry reset instead of leaky beforeAll

- nit: biome format/import-order on all touched files

packages/nodes/src/pipe-trap/definition.ts

@@ -17,6 +17,7 @@ export const pipeTrapDefinition: NodeDefinition<typeof PipeTrapNode> = {
   schema: PipeTrapNode,
   category: 'utility',
   distributionRole: 'fitting',
+  portConnectivityFollow: false, // trap is anchored; dragging a connected run stretches the arm, not the trap
 
   defaults: () => ({
     object: 'node',