fix: System Overview widget - expose monitoring/health endpoints publicly + fix data formats

- Add /api/v1/monitoring/stats and /api/v1/health-checks/status to PUBLIC_ROUTES
  so the frontend widget can fetch without auth
- Transform monitoring stats response from nested {cpu:{percent}} to flat
  {cpu: number, memory: number, memoryUsage: number} for the widget
- Add summary {healthy, unhealthy, total} to health-checks/status response

dashcaddy-api/middleware.js

@@ -305,6 +305,8 @@ module.exports = function configureMiddleware(app, {
     { path: '/api/v1/config',             exact: true,  method: 'GET' },
     { path: '/api/v1/services/status',    exact: true,  method: 'GET' },
     { path: '/api/v1/system/update-notify', exact: true, method: 'POST' },
+    { path: '/api/v1/monitoring/stats',     exact: true, method: 'GET' },
+    { path: '/api/v1/health-checks/status', exact: true, method: 'GET' },
   ];
 
   function isPublicRoute(req) {