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/components/Layout.tsx

@@ -5,6 +5,7 @@
 import React from 'react';
 import { useAuth0 } from '@auth0/auth0-react';
 import { Link, useLocation } from 'react-router-dom';
+import { useLogout } from '../core/auth/useLogout';
 import { Container, Paper, Typography, Box, IconButton, Avatar } from '@mui/material';
 import HomeRoundedIcon from '@mui/icons-material/HomeRounded';
 import DirectionsCarRoundedIcon from '@mui/icons-material/DirectionsCarRounded';
@@ -26,7 +27,8 @@ interface LayoutProps {
 }
 
 export const Layout: React.FC<LayoutProps> = ({ children, mobileMode = false }) => {
-  const { user, logout } = useAuth0();
+  const { user } = useAuth0();
+  const { logout } = useLogout();
   const { sidebarOpen, toggleSidebar, setSidebarOpen } = useAppStore();
   const location = useLocation();
 
@@ -222,7 +224,7 @@ export const Layout: React.FC<LayoutProps> = ({ children, mobileMode = false })
             variant="secondary"
             size="sm"
             className="w-full"
-            onClick={() => logout({ logoutParams: { returnTo: window.location.origin } })}
+            onClick={() => logout()}
           >
             Sign Out
           </Button>