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>

index.php

@@ -47,6 +47,7 @@ if (isset($_GET['sso']) && !dbnToolsIsAuthenticated()) {
 $isAuthed    = dbnToolsIsAuthenticated();
 $userEmail   = $isAuthed ? (string)($_SESSION['dbn_tools_user_email'] ?? '') : '';
 $tools       = dbnToolsLaunchedTools($uiLang);
+$workbench   = dbnToolsWorkbenchMeta($uiLang);
 $langPath    = '/';
 $toolsLogin  = 'https://dobetternorge.no/tools-login.php?return=' . urlencode($returnPath);
 $registerUrl = 'https://dobetternorge.no/register.php';
@@ -147,6 +148,17 @@ window.DBN_TOOLS_LANG = <?= json_encode($uiLang, JSON_UNESCAPED_UNICODE) ?>;
             <p class="lt-tools__sub">Seven purpose-built AI tools &mdash; from audio transcription to deep legal research. Every tool processes your documents in memory and discards them when you&rsquo;re done.</p>
         </div>
         <div class="lt-grid">
+            <a class="lt-card lt-card--workbench" href="<?= $isAuthed ? '/workbench.php' : '#access' ?>" data-tool="workbench">
+                <div class="lt-card__art workbench-entry-art" aria-hidden="true">
+                    <span>WB</span>
+                </div>
+                <div class="lt-card__body">
+                    <p class="lt-card__badge"><?= htmlspecialchars($workbench['badge']) ?></p>
+                    <h3 class="lt-card__title"><?= htmlspecialchars($workbench['label']) ?></h3>
+                    <p class="lt-card__desc"><?= htmlspecialchars($workbench['description']) ?></p>
+                    <span class="lt-card__arrow"><?= htmlspecialchars($isAuthed ? dbnToolsT('enter_workbench', $uiLang) : dbnToolsT('primary_access', $uiLang)) ?> &#x2192;</span>
+                </div>
+            </a>
 <?php foreach ($tools as $slug => $item): ?>
             <a class="lt-card" href="preview.php?tool=<?= htmlspecialchars($slug) ?>" data-tool="<?= htmlspecialchars($slug) ?>">
                 <div class="lt-card__art" aria-hidden="true">