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.

en/odoo-hosting/cheap-odoo-hosting-2026/index.html

@@ -1556,8 +1556,8 @@
 
     <script>
         // Initialize components
-        document.getElementById('header').innerHTML = typeof createHeader === 'function' ? /*W6-static*/null : '';
-        document.getElementById('footer').innerHTML = typeof createFooter === 'function' ? /*W6-static*/null : '';
+        document.getElementById('header').innerHTML = typeof createHeader === 'function' ? createHeader() : '';
+        document.getElementById('footer').innerHTML = typeof createFooter === 'function' ? createFooter() : '';
         // Scroll animation observer
         const observer = new IntersectionObserver((entries) => {
             entries.forEach(entry => {