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

@@ -0,0 +1,21 @@
+import { type NextRequest, NextResponse } from "next/server";
+
+// Edge proxy (formerly "middleware"): Prisma can't run here, so we only forward
+// the request path (so server components / the access guard can read it via
+// headers()) and normalize the real client IP. The DB-backed banned/maintenance
+// checks happen in src/lib/access-guard.ts (Node runtime) from the root layout.
+export function proxy(req: NextRequest) {
+  const headers = new Headers(req.headers);
+  headers.set("x-pathname", req.nextUrl.pathname);
+  const ip =
+    req.headers.get("cf-connecting-ip") ??
+    req.headers.get("x-forwarded-for")?.split(",")[0]?.trim() ??
+    req.headers.get("x-real-ip") ??
+    "";
+  if (ip) headers.set("x-real-client-ip", ip);
+  return NextResponse.next({ request: { headers } });
+}
+
+export const config = {
+  matcher: ["/((?!api|_next/static|_next/image|assets|favicon.ico).*)"],
+};