Moved links have to be rewritten by hand #1255

Where: scripts/check_external_links.py.

Current gap: The report lists each permanent redirect with its new address, and #1230 was a manual search and replace across five files.

Suggested approach: Add --fix-moved that rewrites old -> new in the checked markdown files, skipping ignored URLs and URLs whose final address is a login or error page.

Done when: a test rewrites a link in a temporary document and leaves an ignored one alone.