feat: add admin layout with sub-navigation and routing

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/pages/Admin/Admin.module.css

@@ -0,0 +1,36 @@
+.adminNav {
+  display: flex;
+  gap: 0;
+  border-bottom: 1px solid var(--border-subtle);
+  padding: 0 20px;
+  background: var(--bg-base);
+}
+
+.adminTab {
+  padding: 10px 16px;
+  border: none;
+  background: none;
+  color: var(--text-secondary);
+  font-family: var(--font-body);
+  font-size: 13px;
+  font-weight: 500;
+  cursor: pointer;
+  border-bottom: 2px solid transparent;
+  margin-bottom: -1px;
+  transition: color 0.15s, border-color 0.15s;
+}
+
+.adminTab:hover {
+  color: var(--text-primary);
+}
+
+.adminTabActive {
+  color: var(--amber);
+  border-bottom-color: var(--amber);
+}
+
+.adminContent {
+  flex: 1;
+  overflow-y: auto;
+  padding: 20px;
+}

src/pages/Admin/Admin.tsx

@@ -1,22 +1,51 @@
+import { useNavigate, useLocation } from 'react-router-dom'
 import { AppShell } from '../../design-system/layout/AppShell/AppShell'
 import { Sidebar } from '../../design-system/layout/Sidebar/Sidebar'
 import { TopBar } from '../../design-system/layout/TopBar/TopBar'
-import { EmptyState } from '../../design-system/primitives/EmptyState/EmptyState'
 import { SIDEBAR_APPS } from '../../mocks/sidebar'
+import styles from './Admin.module.css'
+import type { ReactNode } from 'react'
+
+const ADMIN_TABS = [
+  { label: 'User Management', path: '/admin/rbac' },
+  { label: 'Audit Log', path: '/admin/audit' },
+  { label: 'OIDC', path: '/admin/oidc' },
+]
+
+interface AdminLayoutProps {
+  title: string
+  children: ReactNode
+}
+
+export function AdminLayout({ title, children }: AdminLayoutProps) {
+  const navigate = useNavigate()
+  const location = useLocation()
 
-export function Admin() {
   return (
     <AppShell sidebar={<Sidebar apps={SIDEBAR_APPS} />}>
       <TopBar
-        breadcrumb={[{ label: 'Admin' }]}
+        breadcrumb={[
+          { label: 'Admin', href: '/admin' },
+          { label: title },
+        ]}
         environment="PRODUCTION"
-
         user={{ name: 'hendrik' }}
       />
-      <EmptyState
-        title="Admin Panel"
-        description="Admin panel coming soon."
-      />
+      <nav className={styles.adminNav} aria-label="Admin sections">
+        {ADMIN_TABS.map((tab) => (
+          <button
+            key={tab.path}
+            className={`${styles.adminTab} ${location.pathname === tab.path ? styles.adminTabActive : ''}`}
+            onClick={() => navigate(tab.path)}
+            type="button"
+          >
+            {tab.label}
+          </button>
+        ))}
+      </nav>
+      <div className={styles.adminContent}>
+        {children}
+      </div>
     </AppShell>
   )
 }