Brummel
e2e3a51c6c
Replace the hand-rolled aura-cli argv parser with a clap derive parser: scoped `aura <sub> --help`, `--version`/`-V`, a per-flag Options section, and `--flag=value`/`--`/long-opt abbreviation for free. Two iterations — (1) clap migration, behaviour-preserving on exit codes; (2) exit-code split (usage=2, runtime=1). clap is admitted under the C16 per-case review (research-side CLI, invariant 8 untouched). Forks ratified by the user (clap over hand-rolled; GNU-compliance over the machine-first reframe; exit-code Option A) and the three spec-time derived decisions (dual-grammar clap mapping, parse-vs-runtime exit classification, two-iteration split) are recorded on #175. Boss-signed on grounding-check PASS (independent, fresh-context; 13 current-behaviour assumptions all ratified by named green tests). refs #175