feat(branding): re-theme Bootstrap to the brand colour; 3D neon button hover; hide Mensalidades link without plans

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

site/assets/css/style.css

@@ -353,6 +353,51 @@ section[id] {
   color: var(--fitme-accent);
 }
 
+/* ── 3D neon extrusion on hover ────────────────────────────────────────────────
+   The button lifts off the "wall" toward the viewer; the faces it leaves behind
+   (the extruded sides) are drawn with stacked hard shadows in the brand colour
+   and lit like neon tubes (glow on top). Colours come from the gym's brand
+   tokens, so each gym glows in its own colour. */
+.site-btn,
+.gym-switch-btn {
+  --neon: color-mix(in srgb, var(--fitme-accent) 70%, #fff);
+  --neon-edge: var(--fitme-accent-dark);
+  --depth: 7px;
+}
+
+@media (hover: hover) and (prefers-reduced-motion: no-preference) {
+  .site-btn,
+  .gym-switch-btn {
+    transition: transform .18s ease, box-shadow .18s ease, background var(--fitme-transition), color var(--fitme-transition);
+  }
+
+  .site-btn:hover,
+  .site-btn:focus-visible,
+  .gym-switch-btn:hover,
+  .gym-switch-btn:focus-visible {
+    transform: translate(calc(var(--depth) * -1), calc(var(--depth) * -1));
+    box-shadow:
+      1px 1px 0 var(--neon-edge),
+      2px 2px 0 var(--neon),
+      3px 3px 0 var(--neon-edge),
+      4px 4px 0 var(--neon),
+      5px 5px 0 var(--neon-edge),
+      6px 6px 0 var(--neon),
+      7px 7px 0 var(--neon-edge),
+      7px 7px 14px 2px rgba(var(--fitme-accent-rgb), .75),
+      10px 10px 30px 4px rgba(var(--fitme-accent-rgb), .45);
+  }
+
+  .site-btn:active,
+  .gym-switch-btn:active {
+    transform: translate(-2px, -2px);
+    box-shadow:
+      1px 1px 0 var(--neon-edge),
+      2px 2px 0 var(--neon),
+      2px 2px 10px 1px rgba(var(--fitme-accent-rgb), .6);
+  }
+}
+
 /* ── Bootstrap Nav Overrides ───────────────────────────────────────────────── */
 .nav-link {
   font-weight: 700;