fix: refactor breadcrumb partial to WAI-ARIA best-practice pattern

- Replace <div>+<i> structure with <nav aria-label>+<ol>+<li>
- Move separators from DOM to CSS pseudo-elements (li+li::before)
- Add hover/focus-visible states and color differentiation
- Replace hard-coded px values with design tokens
- Explicitly reset shell nav/ol/li rules for self-contained styling
- Add i18n key for breadcrumb nav landmark label

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

templates/partials/app-breadcrumb.phtml

@@ -8,24 +8,25 @@ if (!$items) {
 }
 $lastIndex = count($items) - 1;
 ?>
-<div class="app-breadcrumb">
-  <?php foreach ($items as $index => $item): ?>
-    <?php
-    $label = (string) ($item['label'] ?? '');
-    $href = (string) ($item['href'] ?? '');
-    $path = (string) ($item['path'] ?? '');
-    $isLast = $index === $lastIndex;
-    if ($href === '' && $path !== '') {
-        $href = lurl($path);
-    }
-    ?>
-    <?php if ($href !== '' && !$isLast): ?>
-      <a href="<?php e($href); ?>"><?php e($label); ?></a>
-    <?php else: ?>
-      <span<?php if ($isLast): ?> aria-current="page"<?php endif; ?>><?php e($label); ?></span>
-    <?php endif; ?>
-    <?php if (!$isLast): ?>
-      <i class="bi bi-chevron-right"></i>
-    <?php endif; ?>
-  <?php endforeach; ?>
-</div>
+<nav class="app-breadcrumb" aria-label="<?php e(t('Breadcrumb')); ?>">
+  <ol>
+    <?php foreach ($items as $index => $item): ?>
+      <?php
+      $label = (string) ($item['label'] ?? '');
+      $href = (string) ($item['href'] ?? '');
+      $path = (string) ($item['path'] ?? '');
+      $isLast = $index === $lastIndex;
+      if ($href === '' && $path !== '') {
+          $href = lurl($path);
+      }
+      ?>
+      <li>
+        <?php if ($href !== '' && !$isLast): ?>
+          <a href="<?php e($href); ?>"><?php e($label); ?></a>
+        <?php else: ?>
+          <span<?php if ($isLast): ?> aria-current="page"<?php endif; ?>><?php e($label); ?></span>
+        <?php endif; ?>
+      </li>
+    <?php endforeach; ?>
+  </ol>
+</nav>