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/assets/less/controls/selector-group.less

@@ -0,0 +1,35 @@
+.nav.selector-group {
+    font-size: 13px;
+    letter-spacing: 0.01em;
+    margin-bottom: 20px;
+
+    li {
+        a {
+            padding: 7px 20px 7px 23px;
+            color: #95a5a6;
+        }
+
+        &.active {
+            border-left: 3px solid #e6802b;
+            padding-left: 0;
+
+            a {
+                padding-left: 20px;
+                color: #2b3e50;
+            }
+        }
+
+        i[class^="icon-"] {
+            font-size: 17px;
+            margin-right: 6px;
+            position: relative;
+            top: 1px;
+        }
+    }
+}
+
+div.panel {
+    .nav.selector-group {
+        margin: 0 -20px 20px -20px;
+    }
+}