add handler mapping

whatsapp-router/src/chatHandlers.ts

@@ -0,0 +1,9 @@
+export const chatHandlers: Record<string, string> = {
+  // Example mapping:
+  // '50496210031@c.us': 'http://llm-agent:8000'
+};
+
+export function getHandler(chatId: string | undefined, defaultUrl?: string): string | undefined {
+  if (!chatId) return defaultUrl;
+  return chatHandlers[chatId] || defaultUrl;
+}