feat: VivesPOS landing on Winter CMS 1.2 — theme + plugin + Dockerfile

- Base: wintercms/winter branch 1.2 (full framework)
- Theme vivespos: Canvas 7 + Bootstrap 5 CDN, custom CSS
- Layout: deferred GTM/GA4 tracking, JSON-LD SoftwareApplication
- Partials: hero (offline-first), features, modes (offline/nube toggle),
  screenshots, pricing (3 planes), comparison, FAQ, CTA
- Plugin VivesPOS.Site with ContactForm
- Dockerfile: PHP 8.2 Apache, port 80, healthcheck
- Added winter/wn-pages, blog, sitemap, seo plugins
- Active theme set to vivespos

modules/system/assets/js/snowboard/abstracts/Singleton.js

@@ -0,0 +1,15 @@
+import PluginBase from './PluginBase';
+
+/**
+ * Singleton plugin abstract.
+ *
+ * This is a special definition class that the Snowboard framework will use to interpret the current plugin as a
+ * "singleton". This will ensure that only one instance of the plugin class is used across the board.
+ *
+ * Singletons are initialised on the "domReady" event by default.
+ *
+ * @copyright 2021 Winter.
+ * @author Ben Thomson <git@alfreido.com>
+ */
+export default class Singleton extends PluginBase {
+}