[Bug] kit-translate: flow-style argv (command: [a, b]) parses as an empty command #560

commands:
  - phase: startup
    user: "1000"
    command: [git, config, --global, alias.st, status]

Observed at v4.0.1: kit_spec_commands emits the command record with no argv (__CMD__ startup 1000 false followed directly by __END__), so nothing runs, and acq kit validate reports OK. Block-list argv works.

Expected: parse a single-line flow sequence (it is valid YAML and common in examples), or fail validation with a message pointing at the block-list form.