initrd-shell: fix await_condition command execution

[jaybent]

This fixes #122 which identifies two related bugs in the initrd runtime shell path:

1. await_condition() flattens its command arguments into a scalar with local command="$*" and later executes $command unquoted. This loses argv boundaries and makes the condition sensitive to word splitting and pathname expansion.

2. await_secret_validated() passes [[ ! has_crypt_jobs ]] as if it were a command. That does not call has_crypt_jobs; inside [[ ... ]], has_crypt_jobs is a non-empty string, so the expression is always false.

The fix is to execute "$@" directly in await_condition() and introduce a small has_no_crypt_jobs() predicate for the negated condition.