change middleware to proxy to match conventions

proxy.ts

@@ -1,7 +1,7 @@
 import { NextResponse } from "next/server";
 import type { NextRequest } from "next/server";
 
-export function middleware(request: NextRequest) {
+export function proxy(request: NextRequest) {
     if (request.nextUrl.pathname === '/') {
         return NextResponse.redirect(new URL('/fr', request.url));
     }