feat(corpus): add save-to-corpus + private corpus search scope

- POST /api/save-to-corpus.php — saves tool output text to user's default CaveauAI corpus via ClientRagPipeline
- api/case/upload.php — dual-writes uploaded PDFs to CaveauAI client_documents (best-effort)
- assets/js/corpus-save.js — shared <dialog> handler for .js-save-corpus buttons on all tool pages
- includes/layout_footer.php — injects corpus-save.js + shared save dialog markup
- korrespond/deep-research/barnevernet/discrepancy JS — save-to-corpus buttons on output sections
- api/search.php + LegalTools::search() — corpus_scope param ('shared'|'private'|'both'), merges personal CaveauAI corpus with shared legal library when 'both'
- includes/tool_form.php + assets/js/tools.js — corpus scope radio toggle shown on search tab
- api/user-docs.php — add POST upload method for non-SSO authenticated users

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

includes/layout_footer.php

@@ -26,5 +26,26 @@
 <?php if (!empty($extraScripts) && is_array($extraScripts)): foreach ($extraScripts as $extraScript): ?>
 <script src="<?= htmlspecialchars((string)$extraScript) ?>" defer></script>
 <?php endforeach; endif; ?>
+<script src="assets/js/corpus-save.js" defer></script>
+
+<!-- Save-to-corpus dialog (shared across all tool pages) -->
+<dialog id="save-corpus-dialog" class="save-corpus-dialog">
+  <form method="dialog" id="save-corpus-form">
+    <h3>Save to corpus</h3>
+    <p class="save-corpus-hint">This will be indexed and searchable in your private corpus.</p>
+    <label>
+      <span>Title <span aria-hidden="true">*</span></span>
+      <input id="save-corpus-title" type="text" required placeholder="Give this entry a title…" autocomplete="off">
+    </label>
+    <label>
+      <span>Tags <span class="save-corpus-optional">(comma-separated)</span></span>
+      <input id="save-corpus-tags" type="text" placeholder="e.g. barnevern, 2024, kjennelse">
+    </label>
+    <menu>
+      <button type="submit" class="btn-primary">Save to corpus</button>
+      <button type="button" id="save-corpus-cancel">Cancel</button>
+    </menu>
+  </form>
+</dialog>
 </body>
 </html>