v0.4.3 — --help no longer performs the default action

Security

• --help no longer performs the CLI's default action. All three published CLIs ignored unrecognized arguments and fell through to their default — which for sparkbtcbot-setup is creating a wallet: an agent probing --help for usage silently bootstrapped a real, unbacked wallet (caught by QA on REGTEST before it happened on MAINNET). sparkbtcbot-leaf-vault --help would likewise have taken a snapshot, and a typo'd flag to sparkbtcbot-reveal-mnemonic fell through toward a seed reveal. All three now gate arguments before any side effect: -h/--help prints usage and exits 0 (in reveal's case, before the TTY gate — usage holds no secrets), and any unknown argument fails closed with usage on stderr (exit 2). Regression tests pin that --help creates nothing.