Add a waitlist teaser to the README

Promotes the pre-launch waitlist at ponytail.dev/soon with a NOTE
callout just under the header.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

README.es.md

@@ -35,10 +35,6 @@
 
 ---
 
-<p align="center">
-  <a href="https://ponytail.dev/soon"><img src="assets/waitlist-banner-es.png" alt="Algo nuevo está por llegar, únete a la lista" width="760"></a>
-</p>
-
 Lo conoces. Cola de caballo larga. Lentes ovalados. Lleva más tiempo en la empresa que el control de versiones. Le muestras cincuenta líneas; las mira, no dice nada, y las reemplaza por una.
 
 Ponytail lo pone dentro de tu agente de IA.

README.ko.md

@@ -35,10 +35,6 @@
 
 ---
 
-<p align="center">
-  <a href="https://ponytail.dev/soon"><img src="assets/waitlist-banner-ko.png" alt="새로운 것이 다가오고 있습니다, 대기자 명단 신청" width="760"></a>
-</p>
-
 이런 사람, 다들 알 거다. 긴 포니테일에 타원형 안경. 버전 관리 시스템보다 회사에 오래 있었다. 코드 쉰 줄을 들이밀면 잠깐 보더니, 말없이 한 줄로 바꿔 놓는다.
 
 Ponytail은 그를 당신의 AI 에이전트 안에 앉혀 둔다.

README.md

@@ -35,9 +35,9 @@
 
 ---
 
-<p align="center">
-  <a href="https://ponytail.dev/soon"><img src="assets/waitlist-banner.png" alt="Something's coming, join the waitlist" width="760"></a>
-</p>
+> [!NOTE]
+> **👀 Something new is coming.** The lazy senior dev has been building something. He won't say what yet.
+> **[Be the first to know →](https://ponytail.dev/soon)**
 
 You know him. Long ponytail. Oval glasses. Has been at the company longer than the version control. You show him fifty lines; he looks at them, says nothing, and replaces them with one.