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/registry.go

@@ -0,0 +1,15 @@
+// Package models holds the menu plugin's GORM models.
+package models
+
+var all []any
+
+// Register appends GORM models so later files add models without editing
+// plugin.go.
+func Register(models ...any) {
+	all = append(all, models...)
+}
+
+// All returns every model registered by this package.
+func All() []any {
+	return all
+}