Splits the 138-line static-local kArgRequired array (the list
of flags requiring positional args) into a new
cli_arg_required.{hpp,cpp} module with extern linkage. Then
moves the three meta handlers that depended on it out of
main.cpp into cli_introspect.cpp:
- --validate-cli-help (uses the array for self-check)
- --version / -v (3-line printf)
- --help / -h (1-line passthrough)
main.cpp shrinks by 191 lines (677 to 486). Both the early
missing-argument detector in main() and --validate-cli-help
in cli_introspect.cpp now share one source of truth for the
arg-required list.
