feat(workbench): add DBN Case Workbench guided case-preparation hub

Additive-only change: new workbench.php authenticated page with guided
intake flow, evidence map, tool sequence, output checklist, and
sessionStorage-only note persistence. Dashboard and public index get
a new Case Workbench card. No existing tools, APIs, or prompts modified.

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

dashboard.php

@@ -10,6 +10,7 @@ if (!dbnToolsIsAuthenticated()) {
 
 $uiLang = dbnToolsCurrentLanguage();
 $tools  = dbnToolsLaunchedTools($uiLang);
+$workbench = dbnToolsWorkbenchMeta($uiLang);
 $langPath = '/dashboard.php';
 
 require_once __DIR__ . '/includes/tool-svgs.php';
@@ -73,6 +74,13 @@ window.DBN_TOOLS_LANG = <?= json_encode($uiLang, JSON_UNESCAPED_UNICODE) ?>;
     <div class="disclaimer" role="note"><?= htmlspecialchars(dbnToolsT('disclaimer', $uiLang)) ?></div>
 
     <section class="tool-dashboard-grid" aria-label="Available tools">
+        <a class="dashboard-tool-card dashboard-tool-card--workbench" href="<?= htmlspecialchars($workbench['url']) ?>">
+            <span class="dashboard-tool-card__icon"><?= htmlspecialchars($workbench['icon']) ?></span>
+            <span class="dashboard-tool-card__badge"><?= htmlspecialchars($workbench['badge']) ?></span>
+            <h2><?= htmlspecialchars($workbench['label']) ?></h2>
+            <p><?= htmlspecialchars($workbench['description']) ?></p>
+            <strong><?= htmlspecialchars(dbnToolsT('enter_workbench', $uiLang)) ?></strong>
+        </a>
 <?php foreach ($tools as $slug => $item): ?>
         <a class="dashboard-tool-card" href="<?= htmlspecialchars($item['url']) ?>">
             <span class="dashboard-tool-card__icon"><?= htmlspecialchars($item['icon']) ?></span>