fix: the room_wall_ids invariant applies to model v8 and later again (#316, review r4 H1)

The r3-M1 fix was applied as a mechanical substring replacement and flipped
BOTH model_version conditions in the file; the independent room_wall_ids
invariant (#244/#252) silently stopped checking every v9+ document. Only the
opening_host requirement is scoped to model v8 — room_wall_ids is back to
'v8 and every later version', now pinned by its first regression test
(phantom wall_ids reported on v9 and v8; executed red on the broken
comparison, green after the fix).

Issue: #316
User-Visible: no

scripts/model-invariants.mjs

@@ -225,7 +225,7 @@ export function checkReferences({ config, layout = {} } = {}, { notes = [] } = {
             'комнаты назначения не существует в том же пространстве');
         }
       }
-      if (Number(config?.model_version || 0) === 8) {
+      if (Number(config?.model_version || 0) >= 8) {
         const wallIds = Array.isArray(room?.wall_ids) ? room.wall_ids : [];
         const poly = roomPolygon(room) || [];
         if (wallIds.length !== poly.length) {