fix v1.38.4: derived wall segments trimmed under open boundaries

- the markup layer's .seg lines ran solid through open stretches;
  cutSegments extracted (outlineWithout now reuses it) and applied to
  _segments in _renderMarkupLayer
- smoke_openwall: planSegCut check (15 total); docs same-commit

package.json

@@ -1,6 +1,6 @@
 {
   "name": "houseplan-card",
-  "version": "1.38.3",
+  "version": "1.38.4",
   "description": "Interactive house plan Lovelace card for Home Assistant",
   "license": "MIT",
   "type": "module",