feat: Google News sitemap

- sitemap-news.xml lists the articles (content kind article) first
  published in the last two days, newest first, at most 1000, with the
  publication name (news_publication, else app.name), the language of the
  locale, the publication date and the title
- news_sources narrows it to type:<key> and category:<key>:<id> values;
  the Images and News tab lists the values to use in a partial
- the index lists the file while news_enabled is on; otherwise it is 404

controllers/settings.go

@@ -12,6 +12,7 @@ import (
 	"git.golem15.com/golem15/summercms/modules/cabana"
 	"git.golem15.com/golem15/summercms/modules/pact"
 	"git.golem15.com/golem15/summercms/modules/phrasebook"
+	"git.golem15.com/golem15/summercms/modules/signpost"
 	"gorm.io/gorm"
 )
 
@@ -129,9 +130,76 @@ type reasonRow struct {
 // and the index note; files.empty before the first build and
 // files.building while a rebuild asked for from the admin runs.
 func (c settingsAdminController) PartialData(ctx context.Context, name string, _ any) (any, error) {
-	if name != "sitemap_files" {
-		return nil, nil
+	switch name {
+	case "sitemap_files":
+		return c.filesData(ctx)
+	case "news_sources":
+		return c.newsSourcesData(ctx)
 	}
+	return nil, nil
+}
+
+// sourceRow is one row of the news_sources partial: the value to enter and
+// what it lists.
+type sourceRow struct {
+	Value string
+	Label string
+}
+
+// newsSourcesView is the view model of the news_sources partial.
+type newsSourcesView struct {
+	Rows []sourceRow
+}
+
+// newsSourcesData lists the values the news_sources taglist takes
+// (classes.NewsSources): each article type, then the categories its
+// listed articles name, labelled "<type>: <title>".
+func (c settingsAdminController) newsSourcesData(ctx context.Context) (any, error) {
+	app := appOf(c.app)
+	db, err := database(ctx, c.app)
+	if err != nil {
+		return nil, err
+	}
+	settings, err := classes.LoadSettings(db)
+	if err != nil {
+		return nil, err
+	}
+	var reg *signpost.Registry
+	if app != nil {
+		reg, _ = app.Lookup[*signpost.Registry]()
+	}
+	sources, err := classes.NewsSources(db, reg, models.Text(settings.DefaultLocale))
+	if err != nil {
+		return nil, err
+	}
+	tr := translator(c.app)
+	label := func(key string) string {
+		if reg != nil {
+			if typ, ok := reg.ContentType(key); ok && typ.Label != "" {
+				return Phrase(ctx, tr, typ.Label, nil)
+			}
+		}
+		return key
+	}
+	view := newsSourcesView{}
+	for _, src := range sources {
+		row := sourceRow{Value: src.Value}
+		if src.ID == "" {
+			row.Label = Phrase(ctx, tr, "golem15.sitemap::lang.news.source_type", map[string]string{"type": label(src.Type)})
+		} else {
+			title := src.Title
+			if title == "" {
+				title = src.ID
+			}
+			row.Label = label(src.Type) + ": " + title
+		}
+		view.Rows = append(view.Rows, row)
+	}
+	return view, nil
+}
+
+// filesData is the view of the S1 files partial.
+func (c settingsAdminController) filesData(ctx context.Context) (any, error) {
 	app := appOf(c.app)
 	db, err := database(ctx, c.app)
 	if err != nil {