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>

backend/src/features/auth/api/auth.routes.ts

@@ -48,4 +48,10 @@ export const authRoutes: FastifyPluginAsync = async (
     preHandler: [fastify.authenticate],
     handler: authController.requestPasswordReset.bind(authController),
   });
+
+  // POST /api/auth/track-logout - Track logout event for audit (requires JWT)
+  fastify.post('/auth/track-logout', {
+    preHandler: [fastify.authenticate],
+    handler: authController.trackLogout.bind(authController),
+  });
 };