Mirrors Hare's getopt subject to current cgen gaps: flat `command`
fields instead of slices, struct-not-tuple `option`, error/help
constructors take out-pointers. The `parse` wrapper plus
printusage/printhelp/printsubcmds are deferred (need fmt.fprintf
with {}-interpolation, which lib/fmt doesn't expose yet). SUBCMD
machinery dropped entirely per Drew — accept-but-inert would have
been a silent-misuse hazard.
Graduates in one go when cgen tasks #4#5#6#7#9#10#11#14
land. File header names the three surface sweeps that will follow.
Surfaces task #15 (w6c: && doesn't short-circuit, nil-arg deref
in test exposed it).
