feat(site): slow brand-colour sweep along the bottom of the navbar

site/assets/css/style.css

@@ -537,6 +537,41 @@ section[id] {
   border-bottom: 1px solid rgba(0, 0, 0, .04);
 }
 
+/* Bottom edge: the Mensalidades sweep in the current gym's colour (:root
+   --fitme-accent from gym_brand_css()), always on and much slower. A wide
+   gradient slides along a 2px line (::after); ::before is the same strip
+   blurred, the soft glow under it. Same peak/fade shape as the cards. */
+.header-section::before,
+.header-section::after {
+  content: '';
+  position: absolute;
+  left: 0;
+  right: 0;
+  bottom: -1px;
+  height: 2px;
+  pointer-events: none;
+  background: linear-gradient(90deg,
+      rgba(var(--fitme-accent-rgb), .15) 0%, rgba(var(--fitme-accent-rgb), .15) 30%,
+      var(--fitme-accent) 42%, color-mix(in srgb, var(--fitme-accent) 45%, #fff) 50%, var(--fitme-accent) 58%,
+      rgba(var(--fitme-accent-rgb), .15) 70%, rgba(var(--fitme-accent-rgb), .15) 100%)
+    0 0 / 300% 100% repeat-x;
+  animation: nav-sweep 14s linear infinite;
+}
+.header-section::before {
+  height: 6px;
+  bottom: -4px;
+  filter: blur(6px);
+  opacity: .6;
+}
+
+@keyframes nav-sweep {
+  to { background-position: 150% 0; }
+}
+
+@media (prefers-reduced-motion: reduce) {
+  .header-section::before, .header-section::after { animation: none; }
+}
+
 .site-logo {
   max-width: 150px;
   padding: 12px 0;