feat: sticky Header with persistent contact CTA

lib/content.ts

@@ -72,3 +72,7 @@ export const cierre = {
     linkedin: { label: 'LinkedIn', href: 'https://linkedin.com/in/...' },  // TODO dueña: real URL
   },
 };
+
+export const header = {
+  cta: 'Hablemos',   // short nav CTA → #contacto (the full CTA lives in Hero/Cierre)
+};