feat: centralize breadcrumbs in topbar and remove history navigation

Move breadcrumb rendering from individual page templates into the core
topbar. Each page now sets $breadcrumbs in its action .php file; the
topbar renders it automatically via the shared partial.

- Remove global back/forward buttons and app-nav-history.js component
- Remove Alt+Arrow keyboard shortcuts for history navigation
- Render breadcrumb in topbar-left section (replaces button area)
- Clean up breadcrumb CSS: context-neutral base (flex, no margin)
- Recalculate sticky titlebar offset in details container
- Migrate all 41 pages (core + helpdesk, audit, addressbook, api-docs)
- Add missing breadcrumbs to addressbook detail view
- Update architecture contract tests (nav-history references removed)

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

templates/partials/app-breadcrumb.phtml

@@ -1,6 +1,5 @@
 <?php
-$breadcrumbs = $breadcrumbs ?? [];
-$items = array_values(array_filter($breadcrumbs, static function ($item) {
+$items = array_values(array_filter($breadcrumbs ?? [], static function ($item) {
     return !empty($item['label']);
 }));
 if (!$items) {

templates/partials/app-topbar.phtml

@@ -27,17 +27,16 @@ $moduleSlots = is_array($layoutNav['moduleSlots'] ?? null) ? $layoutNav['moduleS
 $moduleTopbarSlots = is_array($moduleSlots['topbar.right_item'] ?? null) ? $moduleSlots['topbar.right_item'] : [];
 
 ?>
-<header class="app-header" data-app-component="nav-history">
+<header class="app-header">
   <nav class="app-topbar">
-    <ul class="app-topbar-left">
-      <li>
-        <a id="global-back" data-tooltip-pos="bottom" data-tooltip="<?php e(t('Back')); ?> (Alt+←)" title="<?php e(t('Back')); ?> (Alt+←)" aria-label="<?php e(t('Back')); ?> (Alt+←)" href="admin"><i class="bi bi-arrow-left"></i></a>
-      </li>
-      <li>
-        <a id="global-forward" data-tooltip-pos="bottom" data-tooltip="<?php e(t('Forward')); ?> (Alt+→)" title="<?php e(t('Forward')); ?> (Alt+→)" aria-label="<?php e(t('Forward')); ?> (Alt+→)" href="admin"><i class="bi bi-arrow-right"></i></a>
-      </li>
-      <li id="async-messages" role="status" aria-live="polite" aria-hidden="true"></li>
-    </ul>
+    <div class="app-topbar-left">
+      <?php
+      if (is_array($breadcrumbs ?? null) && $breadcrumbs !== []) {
+        require __DIR__ . '/app-breadcrumb.phtml';
+      }
+      ?>
+      <span id="async-messages" role="status" aria-live="polite" aria-hidden="true"></span>
+    </div>
     <div class="app-topbar-center">
       <button type="button" class="app-topbar-search-trigger" data-app-search-trigger aria-label="<?php e(t('Search')); ?>" title="<?php e(t('Search')); ?>">
         <i class="bi bi-search" aria-hidden="true"></i>