1-hour workshop: Fail startup clearly when dependencies or services do not start

Problem

The learner setup depends entirely on the startup scripts, but failure handling can report a misleading success state. In app/scripts/start-app.sh, npm install is not checked before npm run dev starts. In app/scripts/start-app.ps1, a failed Node dependency installation emits a warning and continues. Both scripts wait a fixed five seconds and then print both service URLs without checking that Flask and Astro are ready.

This makes common setup failures look like browser or workshop problems and gives independent learners little actionable feedback.

Suggested change

Make both startup scripts stop on dependency installation failures and verify service/process readiness before announcing success.

Acceptance criteria

• A failed Python or Node dependency install exits nonzero with a clear message.
• Failure of either Flask or Astro stops the other managed process.
• URLs are printed only after both services are ready.
• Cleanup still works on Ctrl+C and partial startup failures.
• macOS/Linux and Windows paths have equivalent behavior.

Empieza con app/scripts/start-app.sh y app/scripts/start-app.ps1, siguiendo la instalación de dependencias, la espera fija de cinco segundos, la salida de las URL de los servicios y las rutas de limpieza. Ejecuta ambos scripts de inicio simulando un fallo en la instalación de Python o Node y en el inicio de Flask o Astro; se considera terminado cuando los fallos tienen un estado distinto de cero y claro, los procesos gestionados se detienen juntos, las URL aparecen solo después de que ambos servicios estén listos y la limpieza sigue funcionando con Ctrl+C o con un inicio parcial.