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/ui/vendor/flag-icon/less/flag-icon-base.less

@@ -0,0 +1,28 @@
+.flag-icon-background {
+  background-size: contain;
+  background-position: 50%;
+  background-repeat: no-repeat;
+}
+
+.flag-icon {
+  .flag-icon-background;
+  position: relative;
+  display: inline-block;
+  width: unit((4 / 3), em);
+  line-height: 1em;
+  &:before {
+    content: "\00a0";
+  }
+  &.flag-icon-squared {
+    width: 1em;
+  }
+}
+
+.flag-icon(@country) {
+  .flag-icon-@{country} {
+    background-image: ~"url(@{flag-icon-css-path}@{flag-icon-rect-path}/@{country}.svg)";
+    &.flag-icon-squared {
+      background-image: ~"url(@{flag-icon-css-path}@{flag-icon-square-path}/@{country}.svg)";
+    }
+  }
+}