scripts/fix_dead_external_links.py was referenced by the Makefile but never
committed, and check_external_links.py did not yet save linkcheck/external.json
(both were working-tree only), so external-fix/external-fix-apply failed on
any fresh clone. The fixer is deliberately conservative: only DNS-failed /
connection-failed / host-unreachable links are auto-commented; .onion links
and ambiguous failures (404/5xx/SSL/refused) go to manual review.
