Add why-ours.php — plain-language explainer page

Explains why Do Better Norge tools give different answers than ChatGPT:
RAG, BM25+vector search, reranker, knowledge graph, fine-tuned model.
Includes EN/NO translations, 5 optimised WebP/JPEG images, new kdoc-compare
and kdoc-graph CSS components. Link added from index.php trust section.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

index.php

@@ -195,6 +195,9 @@ window.DBN_TOOLS_LANG = <?= json_encode($uiLang, JSON_UNESCAPED_UNICODE) ?>;
                 <p><?= htmlspecialchars(dbnToolsT('source_text', $uiLang)) ?></p>
             </div>
         </div>
+        <div style="text-align:center;margin-top:2rem">
+            <a href="/why-ours.php" style="display:inline-block;padding:.6rem 1.4rem;border:1.5px solid rgba(0,32,91,.25);border-radius:8px;font-size:.85rem;font-weight:600;color:var(--dbn-blue,#00205b);text-decoration:none;transition:border-color .2s,background .2s" onmouseover="this.style.background='rgba(0,32,91,.05)'" onmouseout="this.style.background=''">Why our tools give different answers than ChatGPT &rarr;</a>
+        </div>
     </section>
 
 <?php if (!$isAuthed): ?>