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/panels.less

@@ -0,0 +1,24 @@
+// Panels
+
+.panel-variant(@border; @heading-text-color; @heading-bg-color; @heading-border) {
+  border-color: @border;
+
+  & > .panel-heading {
+    color: @heading-text-color;
+    background-color: @heading-bg-color;
+    border-color: @heading-border;
+
+    + .panel-collapse > .panel-body {
+      border-top-color: @border;
+    }
+    .badge {
+      color: @heading-bg-color;
+      background-color: @heading-text-color;
+    }
+  }
+  & > .panel-footer {
+    + .panel-collapse > .panel-body {
+      border-bottom-color: @border;
+    }
+  }
+}