Add `maintenance` (alias `mt`) command with create, list, info, update, and delete subcommands for managing maintenance windows via the Connect RPC API. Extract shared wizard helpers (NotEmpty, HandleFormError, BuildSummary, FetchStatusPages, FetchPageComponents, ValidRFC3339) into `internal/wizard/` and export StatusPageURL from `internal/statuspage/` to eliminate duplication between statusreport and maintenance wizards. Add FormatTimestamp utility to shorten RFC 3339 timestamps in human output (`2006-01-02 15:04 UTC`) across both maintenance and status report commands.