feat: sitemap settings singleton with content types and additional addresses

- one settings tile opening the golem15.sitemap.settings singleton
- Files tab (site address, file size, S1 files partial), Additional
  addresses repeater, Content types tab built from signpost at boot
- golem15_sitemap_types; a type switched off leaves the files (reason type)
- a save validates (errors.*) and dispatches a rebuild after commit

models/type_setting.go

@@ -0,0 +1,27 @@
+package models
+
+import (
+	"time"
+
+	"git.golem15.com/golem15/summercms/modules/lagoon"
+)
+
+// TypeSetting is the sitemap's setting of one signpost content type on
+// golem15_sitemap_types, edited on the settings singleton's Content types
+// tab: whether its records are listed, the file name part of its group
+// (sitemap-<slug>-<n>.xml; "" means the default) and its heading per locale
+// in the HTML sitemap. A type without a row is listed under its default
+// slug.
+type TypeSetting struct {
+	TypeKey   string                             `gorm:"column:type_key;primaryKey"`
+	Include   bool                               `gorm:"column:include"`
+	Slug      string                             `gorm:"column:slug"`
+	Titles    lagoon.Jsonable[map[string]string] `gorm:"column:titles"`
+	UpdatedAt time.Time                          `gorm:"column:updated_at"`
+}
+
+func (TypeSetting) TableName() string { return "golem15_sitemap_types" }
+
+func init() {
+	Register(TypeSetting{})
+}