The rate limiter that was "on" without Redis — and panicking our smoke tests

A Go rate limiter incorrectly enabled Redis mode when Redis was not configured, causing a panic in CI smoke tests. This was due to a misunderstanding of Go's interface behavior with typed-nil values. To fix, ensure that a typed nil is not boxed into an interface. A two-layer defense is recommended: avoid boxing a typed nil at the source and add a check for a nil Redis client before using it.