feat v1.37.0: open boundaries (virtual walls)

- room.open_to symmetric links; 'Open boundary' plan tool toggles the
  shared wall pair under the click (sharedBoundary collinear-overlap
  math + distToSegment pull, same as Split); dashed rendering with an
  amber hot state while the tool is active; Esc -> Draw
- glow: the clip becomes the transitive open zone (openZoneOf BFS,
  either-direction links) + door sectors from the zone's outer walls
- model rooms carry open_to; backend ROOM_SCHEMA open_to: [str]
- +3 unit tests (104), smoke_openwall.mjs (8 checks); docs same-commit

docs/CHANGELOG.md

@@ -1,5 +1,16 @@
 # Changelog
 
+## v1.37.0 — 2026-07-23 (open boundaries — virtual walls)
+- Rooms divided only by zoning can now share an **open boundary**: the new
+  "Open boundary" tool in the Plan editor toggles it with a click on the wall
+  two rooms share. The stretch renders dashed; while the tool is active open
+  boundaries highlight amber. Stored as `room.open_to` links by room id, so
+  redrawing/merging neighbours doesn't break them.
+- In the light-sources fill, light flows through open boundaries freely —
+  transitively across the whole connected zone (kitchen ↔ living ↔ hall as
+  one open space), still limited by the glow radius. Door sectors now work
+  from any outer wall of the zone.
+
 ## v1.36.4 — 2026-07-23
 - Glow: sharper light edge — the pool is fully lit for the inner 80% of the
   radius, the gradient falloff lives only in the outer 20%.