ISO8601 timestamp input fields do not accept "+00:00" as zone designator, only "Z"

Thanks @hampus-fluxer! I have accepted the invitation and submitted the fix in PR #2729: https://github.com/fluxerapp/fluxer/pull/2729 It covers both the client/schema Zod validation (, ) and the Gateway ISO8601 regex/parser in , along with comprehensive unit tests for , , and .