fix(redis): recover topology without sentinel quorum

[wallyxjh]

Summary

• Require Sentinel quorum before accepting startup-time Redis master information.
• When Sentinel is split, inspect Redis kernel roles and use the single actual master if one exists.
• Recover the no-master/double-replica case by falling back to the deterministic default primary.
• Fail fast if Redis kernels report multiple masters, avoiding an unsafe split-brain choice.
• Apply the same startup recovery logic to Redis 5 scripts and add ShellSpec regression coverage.

Test plan

• bash -n addons/redis/scripts/redis-start.sh addons/redis/scripts/redis5-start.sh addons/redis/scripts-ut-spec/redis_start_spec.sh
• /tmp/shellspec-0.28.1/shellspec --load-path ./shellspec --shell bash addons/redis/scripts-ut-spec/redis_start_spec.sh:581 addons/redis/scripts-ut-spec/redis_start_spec.sh:616 addons/redis/scripts-ut-spec/redis_start_spec.sh:647 addons/redis/scripts-ut-spec/redis_start_spec.sh:675 addons/redis/scripts-ut-spec/redis_start_spec.sh:716