What changed

Create React App and react-scripts replaced with the Next.js App Router and Turbopack.
React 16 replaced with React 19.3.0; Next.js 16.3.8 installed. Direct runtime packages use the latest stable npm versions checked on October 3, 2026.
Axios and runtime Random User API requests replaced with bundled demo contacts and local portraits, so the page can render on the server and run without a third-party API connection.
Moment replaced with native Date arithmetic and Intl.DateTimeFormat. UTC timestamps render consistently during server rendering and hydration.
Shave DOM mutation replaced with CSS ellipsis. The old Ionicons CDN font replaced with locally bundled Lucide SVG icons.
Obsolete ReactDOM initialization, CRA service worker, public HTML template, and stale Yarn lockfile removed. npm is the canonical package manager; package-lock.json has been regenerated.
Next.js metadata, manifest, optimized local contact images, accessible buttons, focus indicators, and native modal dialogs added.
Sidebar and messages scroll independently. The composer stays within the message panel. On narrow screens, select a conversation and use the back button to return to the list.