demo: use-client-transport — upgrade to Next.js 16 with Turbopack

Bump next and eslint-config-next from ^15 to ^16. Remove the webpack
extensionAlias config since Turbopack handles .js → .ts resolution
natively. Drop the .js suffix from the local tools import. The
tsconfig.json changes are auto-generated by Next.js 16.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: mschristensen

demo/vercel/react/use-client-transport/next.config.ts

@@ -2,15 +2,6 @@ import type { NextConfig } from 'next';
 
 const nextConfig: NextConfig = {
   serverExternalPackages: ['jsonwebtoken', 'ably'],
-  webpack: (config) => {
-    // @ably/ai-transport source uses .js extensions in imports (standard TS ESM convention).
-    // When the library is linked as source (file:../../), webpack needs to resolve
-    // .js imports to .ts files.
-    config.resolve.extensionAlias = {
-      '.js': ['.ts', '.tsx', '.js'],
-    };
-    return config;
-  },
 };
 
 export default nextConfig;