fix: rename middleware.ts to proxy.ts for Next.js 16 compatibility

Next.js 16 deprecated the "middleware" file convention in favor of "proxy".
This fixes the build warning reported during manual deploy.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

src/proxy.ts

@@ -1,14 +1,10 @@
-// Next.js middleware — authentication gate
-// Redirects unauthenticated users to login for protected routes.
-// Runs at the edge before the page/api handler.
-
 import { NextResponse } from 'next/server';
 import type { NextRequest } from 'next/server';
 import { getToken } from 'next-auth/jwt';
 
 const PUBLIC_PATHS = new Set(['/', '/login', '/register']);
 
-export async function middleware(request: NextRequest) {
+export async function proxy(request: NextRequest) {
   const { pathname } = request.nextUrl;
 
   // Allow public paths, NextAuth API, and static assets