Mark wall rows OUTER in a zero-refinement hierarchy

build_hierarchy(cfg, [], wall_aware=True) left both base wall rows ACTIVE;
the refined path already marked them OUTER. Add the regression test.
Found by native review of eeb90ac.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/unit/test_hierarchy.py

@@ -88,6 +88,9 @@ class LegacyForms(unittest.TestCase):
         one = build_hierarchy(SMALL, [])
         self.assertEqual(one.depth, 1)
         self.assertTrue((one.kinds[0] == r.ACTIVE).all())
+        walled = build_hierarchy(SMALL, [], wall_aware=True)  # regression: no refinement
+        self.assertTrue((walled.kinds[0][[0, -1]] == r.OUTER_GHOST).all())
+        self.assertTrue((walled.kinds[0][1:-1] == r.ACTIVE).all())
 
 
 if __name__ == "__main__":