supervisord.conf was missing [unix_http_server], [supervisorctl], and
[rpcinterface:supervisor] sections, so the Unix socket was never created.
This caused the readiness check to always fail and the container to exit
with "Supervisord failed to start".
- Add missing supervisord socket and RPC configuration sections
- Improve bootstrap readiness check to verify both process and socket
- Add early exit if supervisord process dies unexpectedly
- Simplify supervisorctl calls (config path no longer needed)
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>