Add public showcase landing, doc summary cards, and chunk toggle

- index.php: public showcase landing page (hero, how-it-works, capabilities,
  evidence mock, login form) visible to unauthenticated visitors; full OG/SEO
  meta; app shell hidden behind auth as before
- tools.css: showcase section styles (gradient hero, step cards, capability
  grid, CTA button, evidence mock, footer)
- LegalTools.php: sourceFromChunk() batch-fetches doc_summaries from RAG DB
  for non-private chunks; excerpt shows doc summary when available, falls back
  to raw chunk text; chunk_text field always carries the raw excerpt
- tools.js: renderEvidenceItem() shows doc summary as card body; adds a
  collapsible "View chunk" toggle when summary differs from raw chunk text

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

assets/js/tools.js

@@ -60,7 +60,7 @@ const els = {};
 
 document.addEventListener('DOMContentLoaded', () => {
   Object.assign(els, {
-    gate: document.querySelector('#passcodeGate'),
+    gate: document.querySelector('#publicLanding'),
     app: document.querySelector('#appShell'),
     passcodeForm: document.querySelector('#passcodeForm'),
     loginEmail: document.querySelector('#loginEmail'),
@@ -291,17 +291,26 @@ function renderEvidence(data) {
 function renderEvidenceItem(item) {
   const title = item.title || item.citation || 'Source';
   const body = item.excerpt || item.why_it_matters || item.citation || '';
+  const chunkText = item.chunk_text || '';
   const meta = [
     item.package_or_corpus,
     item.section,
     item.score !== undefined && item.score !== null ? `score ${item.score}` : '',
   ].filter(Boolean).join(' · ');
 
+  const chunkToggle = (chunkText && chunkText !== body) ? `
+    <details class="chunk-details">
+      <summary class="chunk-toggle">View chunk</summary>
+      <pre class="chunk-text">${escapeHtml(chunkText)}</pre>
+    </details>
+  ` : '';
+
   return `
     <article class="source-card">
       <h4>${escapeHtml(title)}</h4>
       ${meta ? `<p class="source-meta">${escapeHtml(meta)}</p>` : ''}
       <p>${escapeHtml(body)}</p>
+      ${chunkToggle}
     </article>
   `;
 }