Add `lite_smoke --keys`: create a fresh wallet and exercise the M4/M5
spend/backup commands (new-address, export, seed, save) against the real linked
SDXL backend, verifying each response's JSON shape with nlohmann. SECRET-SAFE:
seed and private-key VALUES are never printed — only field presence/shape and
counts (no send/shield, which would broadcast).
Verified live (isolated HOME, throwaway wallet shredded after):
new z shape_ok=1 new t shape_ok=1
seed has_seed=1 has_birthday=1 (REDACTED)
export is_array=1 count=4 has_private_key=1 (REDACTED)
save result_success=1
Confirms the controller's newAddress / exportSeed / exportPrivateKeys / save
parsing matches real backend output.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>