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

custom_components/houseplan/manifest.json

@@ -16,5 +16,5 @@
   "issue_tracker": "https://github.com/Matysh/houseplan-card/issues",
   "requirements": [],
   "single_config_entry": true,
-  "version": "1.38.3"
+  "version": "1.38.4"
 }