Fix dashboard container exit on API failure

[schmuecker]

Summary

• make the dashboard entrypoint exit when the embedded hatchet-api process exits
• shut down the sibling process when either hatchet-api or NGINX stops

Why

If hatchet-api fails during startup, for example while RabbitMQ is still refusing connections, NGINX can keep serving static dashboard assets while /api routes return 502. Because the container stays alive, docker compose restart policies do not recover the API.

Validation

• sh -n build/package/dashboard-entrypoint.sh
• docker run --rm nginx:alpine with fake hatchet-api exiting 42; entrypoint exits 42 and stops real NGINX
• docker run --rm nginx:alpine with fake nginx exiting 17; entrypoint exits 17 and stops fake hatchet-api

[vercel]

@schmuecker is attempting to deploy a commit to the Hatchet Team on Vercel.

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