feat(seo): wire internal links between the 17 blog posts and the pages that sell

The blog was an island: zero post→page links to hosting/upgrade/support/courses,
and only one page→post link in the whole site. Posts ranked for nothing while the
old blog host ranked for our long-tail queries.

Posts → pages (26 new in-body contextual links across 17 posts):
each post now carries one or two links to the page that answers its reader's next
question — odoo-hosting-2027, odoo-community-upgrade, support, the workshops hub,
the n8n masterclass, and the plan pricing on index.html#pricing.

Pages → posts (7 pages, one contextual link each):
index.html (OCA section), odoo-hosting-2027, odoo-community-upgrade, support,
workshops/, odoo-n8n-masterclass/, odoo-erp-automation-bootcamp/ now link into the
post that fits their own subject. The clearest miss is fixed — the
community-vs-enterprise-cost post and the odoo-community-upgrade page now link
to each other.

Anchors wrap existing sentences where the text already said the thing; four short
linking sentences were added (index OCA section, support first-steps FAQ, masterclass
lessons, bootcamp included section). No new components, no related-posts widget,
in-body anchors only. English pages only; DE/ES untouched (translator follow-up).

blog/posts/guide-migrate-enterprise.html

@@ -226,7 +226,7 @@
                     <ul>
                         <li>An active Odoo Enterprise subscription key</li>
                         <li>A full database backup of your CE instance</li>
-                        <li>Your ODOO4projects Powerhouse plan (or higher)</li>
+                        <li>Your ODOO4projects <a href="../../index.html#pricing">Powerhouse plan</a> (or higher)</li>
                     </ul>
                     <div class="pro-tip">
                         <strong>Pro Tip:</strong> Always take a backup before