worker-async crashed in a loop with 'No transport supports Messenger DSN
redis://...' because symfony/redis-messenger was never installed — 10x restart
killed the whole stack. Add the package (v7.4.8).
Also harden healthchecks:
- app: hit the real /health route via PHP get_headers (verifies app boots and
serves, not just that port 80 is open)
- workers: confirm the messenger:consume process is alive via busybox ps
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
