fix: make handleMessageUpsert static to fix webhook processing

src/server.ts

@@ -100,7 +100,7 @@ export class WebhookServer {
 		}
 	}
 
-	private static async handleMessageUpsert(data: any) {
+	static async handleMessageUpsert(data: any) {
 		if (!data?.key?.remoteJid || !data.message || !data.message.conversation) {
 			console.log('⚠️ Invalid message format - missing required fields');
 			return;