feat(staging): inbound links so /odoo-staging-environment/ is not an orphan

The copy's 'Into this page' table, applied as single additive sentences:
- support.html: the 'error 500 after a git check in' FAQ answer links
  'test it safely first'.
- blog/posts/speed-run-backup.html: end of the post links
  'what a staging environment is, and why you probably do not need one'.
- odoo-hosting-2027.html: one contextual note by the backup/module rows
  links 'do you need a staging environment?'.
- index.html: one FAQ card 'Do you need an Odoo staging environment?'.
No footer change. No new impeccable finding category.

blog/posts/speed-run-backup.html

@@ -237,6 +237,11 @@ Odoo &gt; Settings &gt; Technical &gt; Scheduled Actions &gt; backup job</code><
                             >Choose a Plan</a
                         >
                     </div>
+                    <p>
+                        A backup is the safety net for a single change. When the change is bigger than one
+                        module, a version upgrade or a migration, a staging environment is worth it. Read
+                        <a href="../../odoo-staging-environment/">what a staging environment is, and why you probably do not need one</a>.
+                    </p>
                 </div>
             </article>
             <div class="post-footer">