feat(17-04): menu plugin admin with registry types, URL checks and tree reorder

- golem15.menu plugin, tables golem15_menu_menus and golem15_menu_menu_entries with the PHP columns plus a nullable url_pattern (D-02)
- MenuEntry BeforeSave ports PHP beforeSave: nest columns 0, menu from the parent, sort_order after the menu's last
- entry type dropdown: url, divider and the signpost registry types; reference depends on type through signpost.ReferenceOptions
- URL scheme allowlist (errors.url_scheme), target _self or _blank, menu and parent cycle checks
- menu filter, toolbar reorder/create/delete and config_reorder.yaml partitioned by menu
- navigation Menus with Menus and Menu entries, permission golem15.menu.manage_menu, en and pl phrasebooks
- TestMenuAdminSmoke

models/menu.go

@@ -0,0 +1,38 @@
+package models
+
+import "time"
+
+// Menu is a named menu stored on golem15_menu_menus, the PHP
+// Golem15\Menu\Models\Menu. Sites address a menu by its unique code.
+type Menu struct {
+	ID        uint        `gorm:"column:id;primaryKey"`
+	Name      string      `gorm:"column:name"`
+	Code      string      `gorm:"column:code"`
+	IsActive  bool        `gorm:"column:is_active"`
+	CSSClass  *string     `gorm:"column:css_class"`
+	Entries   []MenuEntry `gorm:"foreignKey:MenuID" json:"-"`
+	CreatedAt *time.Time  `gorm:"column:created_at"`
+	UpdatedAt *time.Time  `gorm:"column:updated_at"`
+}
+
+func (Menu) TableName() string { return "golem15_menu_menus" }
+
+// MorphName is the PHP class string of the model.
+func (Menu) MorphName() string { return `Golem15\Menu\Models\Menu` }
+
+// Fillable is the list an admin save may set.
+func (Menu) Fillable() []string {
+	return []string{"name", "code", "is_active", "css_class"}
+}
+
+// Rules require a name and a code that no other menu uses.
+func (Menu) Rules() map[string]string {
+	return map[string]string{
+		"name": "required",
+		"code": "required|unique:golem15_menu_menus",
+	}
+}
+
+func init() {
+	Register(Menu{})
+}