chore: migrate from middleware.ts to proxy.ts for Next.js 16 compatibility

Migrate from the deprecated middleware.ts file convention to the new
proxy.ts convention as required by Next.js 16.0.10.

The middleware file convention has been deprecated and renamed to 'proxy'
to better clarify its purpose as a network boundary in front of the app,
and to avoid confusion with Express.js middleware.

Changes:
- Rename apps/site/middleware.ts to apps/site/proxy.ts
- Add named export function 'proxy' instead of default export
- Add NextRequest type import for type safety
- Maintain full compatibility with next-intl internationalization
- Update comments to reflect proxy terminology

This resolves the deprecation warning:
'The middleware file convention is deprecated. Please use proxy instead.'

Refs: https://nextjs.org/docs/messages/middleware-to-proxy

Author: Faizanahmedsy

apps/site/middleware.ts apps/site/proxy.tsapps/site/middleware.ts renamed to apps/site/proxy.ts

@@ -2,7 +2,11 @@ import createMiddleware from 'next-intl/middleware';
 
 import { availableLocaleCodes, defaultLocale } from '#site/next.locales.mjs';
 
-export default createMiddleware({
+// Migrated from middleware.ts to proxy.ts as per Next.js 16 deprecation
+// The middleware file convention is deprecated and has been renamed to proxy
+// See: https://nextjs.org/docs/messages/middleware-to-proxy
+
+export const proxy = createMiddleware({
   // A list of all locales that are supported
   locales: availableLocaleCodes,
 
@@ -17,6 +21,6 @@ export default createMiddleware({
   alternateLinks: false,
 });
 
-// We only want the middleware to run on the `/` route
+// We only want the proxy to run on the `/` route
 // to redirect users to their preferred locale
 export const config = { matcher: ['/'] };