fix(17): T-17-15 refuse an unsafe frontend_url on save and import

- Settings.BeforeValidate answers a cabana validation error on
  frontend_url, so the settings save is a 422 and the row is unchanged
- sitemap:import-winter stops on a frontend_url that
  models.AllowedFrontendURL refuses, before the dry-run branch and before
  any database use; the value is printed quoted
- errors.frontend_url phrase in en and pl
- TestSettingsBeforeValidate, TestWinterSettingsFrontendURL and the save
  and import refusals in the Postgres smokes

models/settings_test.go

@@ -1,11 +1,18 @@
 package models_test
 
 import (
+	"errors"
+	"reflect"
 	"testing"
 
 	"git.golem15.com/golem15/sm-sitemap-plugin/models"
+	"git.golem15.com/golem15/summercms/modules/cabana"
+	"git.golem15.com/golem15/summercms/modules/lagoon"
 )
 
+// cabana calls the hook on a settings save through this interface.
+var _ lagoon.HasBeforeValidate = (*models.Settings)(nil)
+
 // TestAllowedFrontendURL pins the one definition of a frontend_url that may
 // be saved, imported and applied (T-17-15): empty, or an absolute http(s)
 // URL with a host and without whitespace, control characters, a double
@@ -59,3 +66,32 @@ func TestAllowedFrontendURL(t *testing.T) {
 		}
 	}
 }
+
+// TestSettingsBeforeValidate pins the save check of T-17-15: the hook cabana
+// calls on a settings save passes a null, empty or accepted frontend_url and
+// answers a validation error keyed frontend_url for any other value.
+func TestSettingsBeforeValidate(t *testing.T) {
+	text := func(s string) *string { return &s }
+	for _, url := range []*string{nil, text(""), text("https://www.ex.pl/")} {
+		if err := (&models.Settings{FrontendURL: url}).BeforeValidate(nil); err != nil {
+			t.Errorf("BeforeValidate(%q) = %v, want nil", models.Text(url), err)
+		}
+	}
+	want := map[string]any{"frontend_url": []string{"golem15.sitemap::lang.errors.frontend_url"}}
+	for _, url := range []string{
+		"javascript:alert(document.domain)//",
+		`https://x"/><y a="`,
+		"0",
+		" https://www.ex.pl",
+	} {
+		err := (&models.Settings{FrontendURL: &url}).BeforeValidate(nil)
+		var invalid *cabana.ValidationError
+		if !errors.As(err, &invalid) {
+			t.Errorf("BeforeValidate(%q) = %v, want a *cabana.ValidationError", url, err)
+			continue
+		}
+		if !reflect.DeepEqual(invalid.Details, want) {
+			t.Errorf("BeforeValidate(%q) details = %v, want %v", url, invalid.Details, want)
+		}
+	}
+}