[fix] clean CLI error handling — no raw stack traces, reject unknown args #47

Problem

Two bugs in the CLI argument handling:

1. Raw stack traces leak to users — when failproofai policies --install all okay is run with invalid policy names, Node.js dumps a full stack trace instead of a clean error message.

2. Unknown args silently ignored — failproofai policies --list hi ignores both the unknown --list flag and the extra hi argument instead of erroring.