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/pages/SettingsPage.tsx

@@ -5,6 +5,7 @@
 import React, { useState } from 'react';
 import { useAuth0 } from '@auth0/auth0-react';
 import { useNavigate } from 'react-router-dom';
+import { useLogout } from '../core/auth/useLogout';
 import { useUnits } from '../core/units/UnitsContext';
 import { useAdminAccess } from '../core/auth/useAdminAccess';
 import { useProfile, useUpdateProfile } from '../features/settings/hooks/useProfile';
@@ -44,7 +45,8 @@ import CancelIcon from '@mui/icons-material/Cancel';
 import { Card } from '../shared-minimal/components/Card';
 
 export const SettingsPage: React.FC = () => {
-  const { user, logout } = useAuth0();
+  const { user } = useAuth0();
+  const { logout } = useLogout();
   const navigate = useNavigate();
   const { unitSystem, setUnitSystem } = useUnits();
   const { isAdmin, loading: adminLoading } = useAdminAccess();
@@ -73,7 +75,7 @@ export const SettingsPage: React.FC = () => {
   }, [profile, isEditingProfile]);
 
   const handleLogout = () => {
-    logout({ logoutParams: { returnTo: window.location.origin } });
+    logout();
   };
 
   const handleEditProfile = () => {