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).

odoo-hosting-2027.html

@@ -948,7 +948,7 @@
           <details class="cmp-faq">
             <summary class="plausible-event-name=FAQ">Is there a per-user licence?</summary>
             <div class="cmp-a">
-              <p>No. Odoo Community has no per-user licence; our plans are one flat yearly price. Odoo Enterprise, if you bring it, is licensed per user by Odoo S.A.</p>
+              <p>No. <a href="blog/posts/community-vs-enterprise-cost.html">Odoo Community has no per-user licence</a>; our plans are one flat yearly price. Odoo Enterprise, if you bring it, is licensed per user by Odoo S.A.</p>
             </div>
           </details>
         </div>