fix(cd): harden zoxide directory suggestions

internal/config/config_test.go

@@ -30,6 +30,9 @@ func TestDefaultConfigAndState(t *testing.T) {
 	if !cfg.Core.CobraProbeEnabled {
 		t.Errorf("expected cobra probing to be enabled by default")
 	}
+	if cfg.Zoxide.ExtendCd {
+		t.Errorf("expected zoxide cd extension to be disabled by default")
+	}
 
 	// test manual provider registration
 	cfg.AI.Provider = "custom"