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/backend/widgets/mediamanager/partials/_thumbnail-image.php

@@ -0,0 +1,6 @@
+<?php if ($imageUrl): ?>
+    <img src="<?= $imageUrl ?>"/>
+<?php else: ?>
+    <i class="icon-chain-broken" title="<?= e(trans('backend::lang.media.thumbnail_error')) ?>"></i>
+    <p class="thumbnail-error-message"><?= e(trans('backend::lang.media.thumbnail_error')) ?></p>
+<?php endif ?>