fix: add P0 accessibility fixes to sidebar icon bar and search form

- Add :focus-visible outline to icon bar buttons/links (desktop + mobile)
- Add aria-label to icon bar <nav> for screen reader landmark distinction
- Add role="search" to sidebar search form
- Add "Main menu" / "Hauptmenü" translation key

Workflow: A11Y-SIDEBAR-P0-001

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

templates/partials/app-main-aside-icon-bar.phtml

@@ -6,7 +6,7 @@ $layoutAuth = is_array($viewAuth['layout'] ?? null) ? $viewAuth['layout'] : [];
 $hasAdminPanel = layoutHasAdminPanel($layoutAuth);
 ?>
 <aside class="aside-icon-bar" data-app-component="aside-panels" data-aside-storage="app-sidebar-panel">
-    <nav>
+    <nav aria-label="<?php e(t('Main menu')); ?>">
         <ul class="aside-icon-group" role="tablist" aria-orientation="vertical">
             <li>
                 <button type="button" id="aside-tab-explorer" data-aside-target="explorer" role="tab"

templates/partials/app-main-aside.phtml

@@ -343,7 +343,7 @@ $moduleSearchSlots = is_array($moduleSlots['search.resource_item'] ?? null) ? $m
 
         <div id="aside-panel-search" class="app-sidebar-panel" data-app-component="global-search" data-aside-panel="search"
             data-aside-title="<?php e(t('Search')); ?>" role="tabpanel" aria-labelledby="aside-tab-search" hidden>
-            <form class="app-search">
+            <form class="app-search" role="search">
                 <input type="search" name="side-search" id="side-search" placeholder="<?php e(t('Search...')); ?>"
                     aria-label="<?php e(t('Search')); ?>">
                 <span class="app-search-shortcut" data-search-shortcut aria-hidden="true"></span>