Optimise /odoo-ia/ and fix the site-wide 'null' header bug

/odoo-ia/ (279 impressions at position 6.8 for 'odo ia', zero clicks):
- H1 answers the query instead of describing the page: 'Odoo IA: que hace la
  inteligencia artificial en Odoo (y que no)'.
- Hero stats '60+ Recursos / 85% Automatizacion / 24/7 Operacion' replaced with
  the three honest routes: nativo / integracion / fuera. '85%' had no source.
- 'Empieza por aqui': five curated entry points, so the hub is a guide and not
  only a list of 55 links.
- Hosting CTA with utm_medium=hub-cta and a disclosure.
- FAQ (5 questions) + matching FAQPage schema. Answers are conditional on
  version and edition; no feature list is asserted, because odoo.com has no AI
  page to verify one against.

Separately, a real defect found while checking the render: 1,714 script blocks
across 840 pages called document.write(null) or set innerHTML = null, so the
header and footer rendered the literal text 'null'. Replaced with
createHeader()/createFooter(), which restores the real navigation on every
affected page.

odoo/odoo-helpdesk-atencion-cliente-2025/index.html

@@ -129,7 +129,7 @@
 </head>
 <body>
     <script src="/components/header.min.js"></script>
-    <script>document.write(/*W6-static*/null);</script>
+    <script>document.write(createHeader());</script>
     
     <style>
         body {
@@ -854,7 +854,7 @@
     </script>
     
     <script src="/components/footer.min.js"></script>
-    <script>document.write(/*W6-static*/null);</script>
+    <script>document.write(createFooter());</script>
     <script src="/js/cookie-banner.min.js"></script>
     <script src="/js/plausible-events.js" defer></script>
 </body>