feat(cli): run/tui --help, --version, and a help alias

[plombeer31]

What

run is the first command in the top-level help and had no help of its own: run --help,
run -h, tui --help and a bare help all exited 2 with unknown flag / unknown command, and there was no way to ask which version is installed.

Now:

• atomic-agent run --help / -h — usage, every flag with its default, the piping
  behaviour (one-shot vs interactive), /quit & /abort, and the exit-code contract
• atomic-agent tui --help — same shape; also points scripts at run
• atomic-agent --version / -v / version — prints atomic-agent 0.2.1 (from the
  existing getAppVersion())
• atomic-agent help [command] — alias for <command> --help; bare help prints the
  top-level page; unknown targets exit 2

Shape

The HELP constants copy serve-command.ts verbatim in structure, so all subcommand help
pages read alike. --help is parsed as a first-class parse result ({ help: true })
before flag validation, so it always works, and unknown flags still exit 2.

Testing

• 3 unit tests on parseTuiArgs: --help/-h marker, unknown flags still error, and
  every real flag appears in the help text (rot guard)
• End-to-end against the built CLI: run --help exit 0, run -h exit 0, tui --help
  exit 0, --version/-v/version all print the version, help run mirrors
  run --help, help nonsense exits 2, run --nope still exits 2
• npm run lint clean; full build passes

Note: this branch touches parseArgs in run-agent.ts and tui-args.ts, which #141 and
#142 also modify in different regions — whichever merges last may need a trivial rebase.