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/layout/sidepanel.less

@@ -0,0 +1,97 @@
+//
+// Side panel
+// --------------------------------------------------
+
+#layout-side-panel {
+    .fix-button {
+        position: absolute;
+        right: -25px;
+        top: 0;
+        display: none;
+        width: 25px;
+        height: 25px;
+        font-size: 13px;
+        background: #ecf0f1;
+        z-index: 120;
+        .opacity(0.5);
+        .border-radius(~'0 4px 4px 0');
+
+        i {
+            display: block;
+            text-align: center;
+            margin-top: 5px;
+            color: @color-scrollpanel-fix-button;
+        }
+
+        &:hover {
+            text-decoration: none;
+            display: block;
+            .opacity(1)!important;
+        }
+    }
+
+    &:hover {
+        .fix-button {
+            display: block;
+        }
+    }
+
+    .fix-button-content-header .fix-button {
+        top: 46px;
+    }
+
+    .sidepanel-content-header {
+        background: @brand-secondary-darker;
+        color: white;
+        font-size: 15px;
+        padding: 12px 20px 13px;
+        position: relative;
+
+        &:after {
+            .triangle(down, 15px, 8px, @brand-secondary-darker);
+            position: absolute;
+            left: 14px;
+            bottom: -8px;
+        }
+    }
+}
+
+body.side-panel-not-fixed {
+    #layout-side-panel {
+        display: none;
+
+        .fix-button {
+            .opacity(0.5);
+        }
+    }
+}
+
+body.display-side-panel {
+    #layout-side-panel {
+        display: block;
+        position: absolute;
+        // This needs to be higher than the dropdown overlay, otherwise the
+        // mouseout event fires and sidebar hides when opening a dropdown.
+        z-index: @zindex-dropdown;
+        width: 350px;
+        .box-shadow(3px 0px 3px 0 rgba(0, 0, 0, 0.1));
+    }
+}
+
+@media (min-width: @screen-md-min) {
+    body.side-panel-fix-shadow {
+        #layout-side-panel {
+            .box-shadow(none);
+        }
+    }
+}
+
+.touch #layout-side-panel .fix-button {
+    display: none;
+}
+
+@media (max-width: @screen-sm) {
+    #layout-side-panel .fix-button {
+        display: none;
+    }
+}