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).

index.html

@@ -563,6 +563,7 @@
       <div class="container">
         <p class="section-kicker">OCA Modules</p>
         <h2 class="section-title">Our Top OCA Module Picks</h2>
+        <p style="max-width:760px;margin:0 auto 1.5rem;text-align:center;color:rgba(255,255,255,.72);font-size:.95rem;line-height:1.7">Every module on this list is checked by our robots daily; <a href="/blog/posts/track-the-oca-modules-you-actually-use.html">why we track OCA modules</a> explains what the columns mean and how to read them before an upgrade.</p>
         <div class="oca-search-wrap">
           <input type="text" class="oca-search" id="ocaSearch" placeholder="Search modules..." />
         </div>