docs(readme): document local pre-flight for hygiene gates (#3522)

[kyle-sexton]

Closes #3522.

Claim

The mapping table is the local pre-flight path. machine-specific-paths stays a known coverage gap with no in-repo runner.

Basis

#3522 (four CI round-trips on #3503). Confirmed 2026-09-28: find over this checkout still has no *machine-specific* script; ci.yml pins melodic-software/ci-workflows/.github/actions/machine-specific-paths.

As of

2026-09-28

Recheck

ci-workflows publishes a runnable local form of machine-specific-paths, or a maintainer adds an in-repo wrapper or a documented make/script target for the runnable rows.

Test plan

• listed in-repo scripts exist and are executable
• scripts/check-purged-em-dashes.sh

  

[github-actions]

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