feat: implement full admin panel with dashboard, user management, and platform settings

Adds complete super_admin panel with 9 pages and account owner categories page.
Backend includes 5 new DB tables, ~25 API endpoints, settings manager with
in-memory cache, and 29 integration tests. Frontend includes reusable admin
components (DataTable, Pagination, ActionMenu, etc.) with code-split lazy loading.

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

frontend/src/router.tsx

@@ -17,7 +17,20 @@ const SessionHistoryPage = lazy(() => import('@/pages/SessionHistoryPage'))
 const SessionDetailPage = lazy(() => import('@/pages/SessionDetailPage'))
 const SettingsPage = lazy(() => import('@/pages/SettingsPage'))
 const AccountSettingsPage = lazy(() => import('@/pages/AccountSettingsPage'))
-const AdminCategoriesPage = lazy(() => import('@/pages/AdminCategoriesPage'))
+// Admin pages
+const AdminLayout = lazy(() => import('@/components/admin/AdminLayout'))
+const AdminDashboardPage = lazy(() => import('@/pages/admin/DashboardPage'))
+const AdminUsersPage = lazy(() => import('@/pages/admin/UsersPage'))
+const AdminInviteCodesPage = lazy(() => import('@/pages/admin/InviteCodesPage'))
+const AdminAuditLogsPage = lazy(() => import('@/pages/admin/AuditLogsPage'))
+const AdminPlanLimitsPage = lazy(() => import('@/pages/admin/PlanLimitsPage'))
+const AdminFeatureFlagsPage = lazy(() => import('@/pages/admin/FeatureFlagsPage'))
+const AdminSettingsPage = lazy(() => import('@/pages/admin/SettingsPage'))
+const AdminGlobalCategoriesPage = lazy(() => import('@/pages/admin/GlobalCategoriesPage'))
+
+// Account pages
+const AccountLayout = lazy(() => import('@/components/account/AccountLayout'))
+const TeamCategoriesPage = lazy(() => import('@/pages/account/TeamCategoriesPage'))
 
 export const router = createBrowserRouter([
   {
@@ -108,22 +121,110 @@ export const router = createBrowserRouter([
         ),
       },
       {
-        path: 'account',
+        path: 'account-settings',
         element: (
           <Suspense fallback={<PageLoader />}>
             <AccountSettingsPage />
           </Suspense>
         ),
       },
+      // Admin routes
       {
-        path: 'admin/categories',
+        path: 'admin',
         element: (
           <Suspense fallback={<PageLoader />}>
             <ProtectedRoute requiredRole="super_admin">
-              <AdminCategoriesPage />
+              <AdminLayout />
             </ProtectedRoute>
           </Suspense>
         ),
+        children: [
+          {
+            index: true,
+            element: (
+              <Suspense fallback={<PageLoader />}>
+                <AdminDashboardPage />
+              </Suspense>
+            ),
+          },
+          {
+            path: 'users',
+            element: (
+              <Suspense fallback={<PageLoader />}>
+                <AdminUsersPage />
+              </Suspense>
+            ),
+          },
+          {
+            path: 'invite-codes',
+            element: (
+              <Suspense fallback={<PageLoader />}>
+                <AdminInviteCodesPage />
+              </Suspense>
+            ),
+          },
+          {
+            path: 'audit-logs',
+            element: (
+              <Suspense fallback={<PageLoader />}>
+                <AdminAuditLogsPage />
+              </Suspense>
+            ),
+          },
+          {
+            path: 'plan-limits',
+            element: (
+              <Suspense fallback={<PageLoader />}>
+                <AdminPlanLimitsPage />
+              </Suspense>
+            ),
+          },
+          {
+            path: 'feature-flags',
+            element: (
+              <Suspense fallback={<PageLoader />}>
+                <AdminFeatureFlagsPage />
+              </Suspense>
+            ),
+          },
+          {
+            path: 'settings',
+            element: (
+              <Suspense fallback={<PageLoader />}>
+                <AdminSettingsPage />
+              </Suspense>
+            ),
+          },
+          {
+            path: 'categories',
+            element: (
+              <Suspense fallback={<PageLoader />}>
+                <AdminGlobalCategoriesPage />
+              </Suspense>
+            ),
+          },
+        ],
+      },
+      // Account routes
+      {
+        path: 'account',
+        element: (
+          <Suspense fallback={<PageLoader />}>
+            <ProtectedRoute requiredRole="owner">
+              <AccountLayout />
+            </ProtectedRoute>
+          </Suspense>
+        ),
+        children: [
+          {
+            path: 'categories',
+            element: (
+              <Suspense fallback={<PageLoader />}>
+                <TeamCategoriesPage />
+              </Suspense>
+            ),
+          },
+        ],
       },
     ],
   },