Prepare site for React 19.3 release

Author: samselikoff

src/components/MDX/Sandpack/template.ts

@@ -35,8 +35,8 @@ root.render(
           eject: 'react-scripts eject',
         },
         dependencies: {
-          react: '^19.2.1',
-          'react-dom': '^19.2.1',
+          react: '^19.3.0',
+          'react-dom': '^19.3.0',
           'react-scripts': '^5.0.0',
         },
       },

src/components/MDX/SandpackWithHTMLOutput.tsx

@@ -56,8 +56,8 @@ export default function formatHTML(markup) {
 const packageJSON = `
 {
   "dependencies": {
-    "react": "^19.2.1",
-    "react-dom": "^19.2.1",
+    "react": "^19.3.0",
+    "react-dom": "^19.3.0",
     "react-scripts": "^5.0.0",
     "html-format": "^1.1.2"
   },