feat(frontend): add collapsible navigation sidebar

Persist the desktop sidebar state, provide accessible compact navigation tooltips, and cover the collapsed navigation markup with a focused component test.

frontend/src/i18n/messages.ts

@@ -269,6 +269,8 @@ export const messages = {
     'nav.group.account': '账户',
     'nav.group.management': '管理',
     'nav.group.system': '系统',
+    'nav.collapseSidebar': '收起侧边栏',
+    'nav.expandSidebar': '展开侧边栏',
     'nav.dashboard': '仪表盘',
     'nav.healthMonitor': '健康监控',
     'nav.modelCatalog': '模型目录',
@@ -580,6 +582,8 @@ export const messages = {
     'nav.group.account': 'Account',
     'nav.group.management': 'Management',
     'nav.group.system': 'System',
+    'nav.collapseSidebar': 'Collapse sidebar',
+    'nav.expandSidebar': 'Expand sidebar',
     'nav.dashboard': 'Dashboard',
     'nav.healthMonitor': 'Health monitor',
     'nav.modelCatalog': 'Model catalog',