refactor: migrate middleware.ts to proxy.ts (Next.js 16)

Renamed middleware convention to proxy as per Next.js 16 deprecation warning.
- Renamed src/middleware.ts to src/proxy.ts
- Renamed exported function from middleware() to proxy()

src/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) {
     // Define public paths that don't require authentication
     const publicPaths = [
         '/login',