Rename edge middleware.ts -> proxy.ts (Next 16 convention)

Next 16 deprecated the middleware file convention in favour of proxy.ts
with an exported `proxy` function. Same header-forwarding logic and
matcher; clears the build-time deprecation warning.

src/proxy.ts

@@ -1,10 +1,10 @@
 import { type NextRequest, NextResponse } from "next/server";
 
-// Edge middleware: Prisma can't run here, so we only forward the request path
+// Edge proxy (formerly "middleware"): Prisma can't run here, so we only forward
-// (so server components / the access guard can read it via headers()) and
+// the request path (so server components / the access guard can read it via
-// normalize the real client IP. The DB-backed banned/maintenance checks happen
+// headers()) and normalize the real client IP. The DB-backed banned/maintenance
-// in src/lib/access-guard.ts (Node runtime) from the root layout.
+// checks happen in src/lib/access-guard.ts (Node runtime) from the root layout.
-export function middleware(req: NextRequest) {
+export function proxy(req: NextRequest) {
   const headers = new Headers(req.headers);
   headers.set("x-pathname", req.nextUrl.pathname);
   const ip =