emcli had only raw flag usage and no command listing; `--help` on agent commands
even emitted a JSON error envelope and exited 2. Add real help:
- Top-level `emcli` / `help` / `-h` / `--help` prints a grouped command catalogue
(agent vs admin) with one-line summaries and the EMCLI_KEY/EMCLI_DB env vars.
- `emcli help <command>` prints that command's synopsis + summary.
- `emcli <command> --help` prints synopsis + summary + flags and exits 0. Agent
commands keep stdout JSON-free (usage goes to stderr); admin commands print to
stdout. Help works without EMCLI_KEY (no DB access).
- help.go holds the command catalogue; flag.ErrHelp is handled as success, and
admin handlers short-circuit help before opening the store.
Unknown commands still error (exit 2). Full suite passes.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
