Add Deep Research tool — agent + rank/rerank RAG

New surface at /deep-research.php where the user pastes a question or
uploads PDF/DOCX/TXT case files and a LLM-orchestrated agent researches
the Do Better Norge legal corpus from 3-5 angles, with hybrid retrieval,
cross-encoder rerank, and synthesis that emits an inline-[n]-cited
markdown brief plus a numbered sources panel.

Uploaded documents are chunked + embedded in memory only (nomic-embed-text
via LiteLLM) and searched alongside the shared corpus during the same
request — never persisted to disk, DB, or Qdrant.

Reuses ClientRagPipeline::searchAll (hybrid + rerank), dbnV6 slice
helpers, and the existing extract.php text-extraction logic via a new
dbnToolsExtractUploadedFile() helper. Also adds dbnToolsCallGpuLlm()
helper in bootstrap.php — fixes a latent bug where LegalTools.php
was already calling that name with no definition.

Search.php is unchanged.

includes/layout_footer.php

@@ -18,5 +18,8 @@
     </section><!-- /workspace -->
 </main><!-- /appShell -->
 <script src="assets/js/tools.js" defer></script>
+<?php if (!empty($extraScripts) && is_array($extraScripts)): foreach ($extraScripts as $extraScript): ?>
+<script src="<?= htmlspecialchars((string)$extraScript) ?>" defer></script>
+<?php endforeach; endif; ?>
 </body>
 </html>