Fix ModeEntry.prop_z_mean attribute error (use getattr)

app.py

@@ -771,7 +771,8 @@ def _mode_choices_searchable(sibling):
     m = MODELS[sibling]
     out = []
     for md in m.modes:
-        z = f"  z={md.prop_z_mean:+.2f}" if isinstance(md.prop_z_mean, (int, float)) else ""
+        pz = getattr(md, "prop_z_mean", None)
+        z = f"  z={pz:+.2f}" if isinstance(pz, (int, float)) else ""
         out.append((f"[{md.kind}] {md.label} ({md.mode_id}, n={md.n_members}{z})", md.mode_id))
     return sorted(out, key=lambda x: x[0].lower())