Add Google Analytics (G-KZRMDX3JN0)

Author: Sai Sridhar

frontend/pages/_document.tsx

@@ -11,6 +11,13 @@ export default function Document() {
           rel="stylesheet"
         />
         <link rel="icon" href="/favicon.ico" />
+        <script async src="https://www.googletagmanager.com/gtag/js?id=G-KZRMDX3JN0" />
+        <script dangerouslySetInnerHTML={{ __html: `
+          window.dataLayer = window.dataLayer || [];
+          function gtag(){dataLayer.push(arguments);}
+          gtag('js', new Date());
+          gtag('config', 'G-KZRMDX3JN0');
+        `}} />
         <meta name="description" content="Mailair - AI-powered email thread management for service businesses" />
         <link rel="manifest" href="/manifest.json" />
         <meta name="theme-color" content="#7C3AED" />