* fix(redis): add REDIS_CLUSTER_SAFE_DELETE for ElastiCache Serverless CROSSSLOT errors
ElastiCache Serverless and similar managed Redis services present a single-node
connection endpoint but shard keys internally. When USE_REDIS_CLUSTER=false (as
required for single-endpoint services), batchDeleteKeys() uses multi-key DEL
commands that fail with CROSSSLOT errors because the managed cluster rejects
cross-slot operations.
Adds REDIS_CLUSTER_SAFE_DELETE=true which forces per-key deletion (the same
cluster-safe path) without changing the connection mode. This makes the delete
strategy independent of the connection topology.
Closes#13261
* test(cache): add REDIS_CLUSTER_SAFE_DELETE config tests
* fix: Avoid nested Redis delete mode ternary
* docs: Add Redis cluster-safe delete env example
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Co-authored-by: Danny Avila <danny@librechat.ai>