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>

modules/api-docs/pages/api-docs/index().php

@@ -8,4 +8,8 @@ Guard::requireLogin();
 Guard::requireAbilityOrForbidden(ApiDocsAuthorizationPolicy::ABILITY_VIEW);
 
 Buffer::set('title', t('API docs'));
+$breadcrumbs = [
+    ['label' => t('Home'), 'path' => 'admin'],
+    ['label' => t('API docs')],
+];
 Buffer::set('style_groups', json_encode(['api-docs']));

modules/api-docs/pages/api-docs/index(default).phtml

@@ -1,10 +1,5 @@
 <?php
-$breadcrumbs = [
-  ['label' => t('Home'), 'path' => 'admin'],
-  ['label' => t('API docs')],
-];
 $specUrl = lurl('admin/api-docs/spec');
-require templatePath('partials/app-breadcrumb.phtml');
 ?>
 
 <div class="app-swagger-container">