fix(i18n): localise extensionless directory links in the DE/ES pages

build-i18n.py's rebase_paths() only re-pointed a root-absolute page link when it
contained ".html", so extensionless directory links stayed on the EN route even
when the language had its own copy (`/odoo-erp-automation-bootcamp/` on all four
DE and ES pages, and `/` on the DE/ES bootcamp pages). Same guard as the .html
branch: localise only when <lang>/<path>/index.html exists.

Re-applied the rebasing to the 8 already-built DE/ES pages (work/i18n/
relocalise-links.py) - a full re-transform is not safe for them because the
switcher-slot/hero rework means repo pages are not raw transform output. 18 refs
in 8 files. The DE/ES homepages were the stale case: their body links were built
before support.html/odoo-hosting-2027.html existed in that language and were
never revisited.

check-links.py now flags an EN-route page link whose language has its own copy:
0 such links on all 10 DE/ES pages after the rebuild. test-build.py 107 passed;
verify-html.py 0 problems.

de/odoo-hosting-2027.html

@@ -985,7 +985,7 @@
           <div>
             <h4>Nützliche Links</h4>
             <ul>
-              <li><a href="/odoo-erp-automation-bootcamp/">ODOO Bootcamp</a></li>
+              <li><a href="/de/odoo-erp-automation-bootcamp/">ODOO Bootcamp</a></li>
               <li><a href="/de/odoo-hosting-2027.html">ODOO Hosting in 2027</a></li>
               <li><a href="/de/support.html">Support</a></li>
               <li><a href="/legal.html">Rechtliches</a></li>