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

themes/demo/assets/vendor/bootstrap/less/mixins.less

@@ -0,0 +1,40 @@
+// Mixins
+// --------------------------------------------------
+
+// Utilities
+@import "mixins/hide-text.less";
+@import "mixins/opacity.less";
+@import "mixins/image.less";
+@import "mixins/labels.less";
+@import "mixins/reset-filter.less";
+@import "mixins/resize.less";
+@import "mixins/responsive-visibility.less";
+@import "mixins/size.less";
+@import "mixins/tab-focus.less";
+@import "mixins/reset-text.less";
+@import "mixins/text-emphasis.less";
+@import "mixins/text-overflow.less";
+@import "mixins/vendor-prefixes.less";
+
+// Components
+@import "mixins/alerts.less";
+@import "mixins/buttons.less";
+@import "mixins/panels.less";
+@import "mixins/pagination.less";
+@import "mixins/list-group.less";
+@import "mixins/nav-divider.less";
+@import "mixins/forms.less";
+@import "mixins/progress-bar.less";
+@import "mixins/table-row.less";
+
+// Skins
+@import "mixins/background-variant.less";
+@import "mixins/border-radius.less";
+@import "mixins/gradients.less";
+
+// Layout
+@import "mixins/clearfix.less";
+@import "mixins/center-block.less";
+@import "mixins/nav-vertical-align.less";
+@import "mixins/grid-framework.less";
+@import "mixins/grid.less";