feat: Add login/logout audit logging (refs #10)

Backend:
- Add login event logging to getUserStatus() controller method
- Create POST /auth/track-logout endpoint for logout tracking

Frontend:
- Create useLogout hook that wraps Auth0 logout with audit tracking
- Update all logout locations to use the new hook (SettingsPage,
  Layout, MobileSettingsScreen, useDeletion)

Login events are logged when the frontend calls /auth/user-status after
Auth0 callback. Logout events are logged via fire-and-forget call to
/auth/track-logout before Auth0 logout.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/features/settings/mobile/MobileSettingsScreen.tsx

@@ -1,5 +1,6 @@
 import React, { useState } from 'react';
 import { useAuth0 } from '@auth0/auth0-react';
+import { useLogout } from '../../../core/auth/useLogout';
 import { GlassCard } from '../../../shared-minimal/components/mobile/GlassCard';
 import { MobileContainer } from '../../../shared-minimal/components/mobile/MobileContainer';
 import { useSettings } from '../hooks/useSettings';
@@ -75,7 +76,8 @@ const Modal: React.FC<ModalProps> = ({ isOpen, onClose, title, children }) => {
 };
 
 export const MobileSettingsScreen: React.FC = () => {
-  const { user, logout } = useAuth0();
+  const { user } = useAuth0();
+  const { logout } = useLogout();
   const { navigateToScreen } = useNavigationStore();
   const { settings, updateSetting, isLoading, error } = useSettings();
   const { data: profile, isLoading: profileLoading } = useProfile();
@@ -98,11 +100,7 @@ export const MobileSettingsScreen: React.FC = () => {
   }, [profile, isEditingProfile]);
 
   const handleLogout = () => {
-    logout({
-      logoutParams: {
-        returnTo: window.location.origin
-      }
-    });
+    logout();
   };
 
   const handleExportData = () => {