fix(MM-67): address PR review — fmt-check flag, clippy comment, CLAUDE.md alignment
- fmt-check: drop legacy -- separator (cargo fmt --all --check)
- clippy comment: clarify that -D warnings promotes all compiler warnings,
not just Clippy lints
- docker-build comment: add macOS escape hatch note (use remote Linux builder or CI)
- Remove self-evident comments on check, build, test, fmt, run-relay
- CLAUDE.md: align clippy and fmt --check commands with justfile