docs: AGENTS.md commands to pnpm (no npm)

Last leftover npm reference after the pnpm migration (3f0a15e);
README.md was already migrated. Also states pnpm as the required
package manager.

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

AGENTS.md

@@ -25,7 +25,8 @@ One-page landing para **creeer**, marca personal de una estratega de crecimiento
 - `output: export` → HTML estático, **sin backend**
 - Contacto por enlaces directos (WhatsApp, email, LinkedIn) — **sin formulario**
 - Deploy: Vercel o Netlify
-- Comandos: se definen al scaffold (`npm run dev`, `npm run build`, `npm run lint`)
+- Gestor de paquetes: **pnpm** (no npm) — `pnpm@11.7.0` vía `packageManager` / corepack
+- Comandos: `pnpm dev`, `pnpm build`, `pnpm lint`, `pnpm test`
 
 ## Skills relevantes para este proyecto