feat: initial commit — asaas-checkout template white-label

Template genérico de checkout com ASAAS, parametrizado via env vars.
Inclui fluxo completo: checkout → pedido → polling → webhook → admin.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/api/webhook/route.ts

@@ -0,0 +1,6 @@
+// Rota legada do Stripe — substituída por /api/asaas-webhook
+import { NextResponse } from "next/server"
+
+export async function POST() {
+  return NextResponse.json({ message: "Use /api/asaas-webhook" }, { status: 410 })
+}