feat: enhance proxy function with session cookie validation

- Updated the proxy function to accept a NextRequest parameter and check for session cookies.
- Implemented redirection to the sign-in page if no valid session cookie is found.
- Adjusted the matcher configuration to apply the proxy only to the '/dashboard' route.

Author: 0xdevcollins

proxy.ts

@@ -1,9 +1,15 @@
+import { getSessionCookie } from 'better-auth/cookies';
+import type { NextRequest } from 'next/server';
 import { NextResponse } from 'next/server';
 
-export async function proxy() {
+export async function proxy(request: NextRequest) {
+  const cookies = getSessionCookie(request);
+  if (!cookies) {
+    return NextResponse.redirect(new URL('/auth?mode=signin', request.url));
+  }
   return NextResponse.next();
 }
 
 export const config = {
-  matcher: ['/'],
+  matcher: ['/dashboard'],
 };