fix(docker): tolerate unavailable IPv6 loopback

[nightcityblade]

Summary

Fixes #2078.

Make Redis's IPv6 loopback bind optional while retaining mandatory IPv4 loopback binding. Redis therefore starts on IPv4-only hosts instead of aborting when ::1 is unavailable, while continuing to listen on IPv6 loopback where supported.

List of files changed and why

• deploy/docker/supervisord.conf - Prefix the IPv6 loopback address with Redis's optional-address marker.
• deploy/docker/tests/test_security_container_posture.py - Require the IPv4 loopback plus optional IPv6 bind form in the container posture test.

How Has This Been Tested?

• PYTHONPATH=. pytest -q deploy/docker/tests/test_security_container_posture.py — 19 passed.
• PYTHONPATH=. pytest -q deploy/docker/tests/test_security_*.py — 316 passed, 1 expected xfail.
• black --check --target-version py312 --line-ranges 77-84 deploy/docker/tests/test_security_container_posture.py — passed.
• git diff --check — passed.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas — N/A; the existing comment already describes the loopback-only Redis binding.
• I have made corresponding changes to the documentation — N/A; this corrects container startup behavior without changing the documented interface.
• I have added/updated unit tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes