Add real Redis Sentinel, Cluster, authentication, and TLS tests

[hemju]

Gap

Redis integration and soak tests exercise only standalone redis:7-alpine. Sentinel/Cluster coverage is limited to key-slot and client-option unit tests even though both topologies are advertised as first-class.

Acceptance criteria

• Test a real Redis Cluster with reshard/topology refresh and master failover.
• Test a real Sentinel deployment with leader failover.
• Cover ACL authentication, TLS certificate verification, and invalid credentials.
• Run the shared 78-test store contract where topology semantics permit.
• Add bounded CI smoke coverage plus longer opt-in failover/soak tasks.