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/less/global.mixins.triangle.less

@@ -0,0 +1,34 @@
+// Triangles
+// --------------------------------------------------
+
+.triangle-base() {
+    content: '';
+    display: block;
+    width: 0;
+    height: 0;
+}
+.triangle(@direction, @width, @height, @color) when (@direction = up) {
+    .triangle-base();
+    border-left: (@width / 2) solid transparent;
+    border-right: (@width / 2) solid transparent;
+    border-bottom: @height solid @color;
+}
+.triangle(@direction, @width, @height, @color) when (@direction = down) {
+    .triangle-base();
+    border-left: (@width / 2) solid transparent;
+    border-right: (@width / 2) solid transparent;
+    border-top: @height solid @color;
+    border-bottom-width: 0;
+}
+.triangle(@direction, @width, @height, @color) when (@direction = left) {
+    .triangle-base();
+    border-top: (@height / 2) solid transparent;
+    border-bottom: (@height / 2) solid transparent;
+    border-right: @width solid @color;
+}
+.triangle(@direction, @width, @height, @color) when (@direction = right) {
+    .triangle-base();
+    border-top: (@height / 2) solid transparent;
+    border-bottom: (@height / 2) solid transparent;
+    border-left: @width solid @color;
+}