[Bug] acq kit validate reports OK for commands the translator will skip or run empty #563

kit_validate accepts a spec that kit_spec_commands then drops or empties at apply time, so validation gives no signal for the most common authoring slips:

• a trailing comment on phase: or user: (command skipped with only a stderr warning at create; see [Bug] kit-translate: a trailing # comment is kept in top-level fields and commands[] (command silently skipped) #558);
• flow-style argv, command: [echo, four] (parsed as an empty argv; see [Bug] kit-translate: flow-style argv (command: [a, b]) parses as an empty command #560);
• a trailing comment after an argv item (argument changed).

Fixture: the spec in #558 plus command: [echo, four]. Observed at v4.0.1: kit: validate: OK.

Expected: kit validate runs the same kit_spec_commands parse and fails when a declared command is skipped, has an empty argv, or (until comments are stripped) carries a # in phase:, user:, or an argv item.