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>

assets/js/tools.js

@@ -910,6 +910,7 @@ document.addEventListener('DOMContentLoaded', () => {
     uploadFileList: document.querySelector('#uploadFileList'),
     uploadClear: document.querySelector('#uploadClear'),
     aliasSection: document.querySelector('#aliasSection'),
+    corpusScopeControl: document.querySelector('#corpusScopeControl'),
     addAliasRow: document.querySelector('#addAliasRow'),
     aliasRows: document.querySelector('#aliasRows'),
     audioZone: document.querySelector('#audioZone'),
@@ -1013,6 +1014,7 @@ function setTool(toolName) {
     els.input.placeholder = tool.placeholder;
   }
   els.languageControl.classList.toggle('is-hidden', !tool.usesLanguage);
+  els.corpusScopeControl?.classList.toggle('is-hidden', toolName !== 'search');
   els.redactionControl.classList.toggle('is-hidden', toolName !== 'redact');
   els.uploadZone.classList.toggle('is-hidden', toolName !== 'redact' && toolName !== 'timeline');
   els.aliasSection.classList.toggle('is-hidden', toolName !== 'redact');
@@ -1080,6 +1082,7 @@ async function runTool(event) {
   }
   if (state.activeTool === 'search') {
     payload.limit = 7;
+    payload.corpus_scope = currentCorpusScope();
   }
   if (state.activeTool === 'redact') {
     lastOriginalText = text;
@@ -1329,6 +1332,10 @@ function currentLanguage() {
   return document.querySelector('input[name="language"]:checked')?.value || 'en';
 }
 
+function currentCorpusScope() {
+  return document.querySelector('input[name="corpusScope"]:checked')?.value || 'both';
+}
+
 function currentRedactionMode() {
   return document.querySelector('input[name="redactionMode"]:checked')?.value || 'standard';
 }