Release v1.56.4

🛠️ Fixes

• Kafka Stale Admin Connection — Kafka subscribers got permanently stuck on "kafka client not connected" after the broker closed an idle TCP connection (default connections.max.idle.ms = 10m). The admin multiConn was dialed only once during initialize() and retryConnect() only covered initial startup, so every Subscribe / Query call failed for the rest of the process lifetime. Added ensureConnected(ctx) which detects a stale admin conn at the entry of Subscribe / Query, re-dials the broker list, and swaps in a fresh multiConn while leaving the writer and per-topic readers untouched so in-flight work isn't disrupted. No public API change.

• SwaggerUI Panic on Files Without Extension — SwaggerUIHandler panicked with an index out of bounds error when serving filenames that had no extension, due to strings.Split + direct index access on the result. Replaced with filepath.Ext for safe extraction, and the handler now returns a defined errMissingFileExtension instead of panicking.