ci: ignore link checker false positives

[7etsuo]

Summary

• Add exact Lychee ignore patterns for tutorial hosts that are live locally but fail from GitHub Actions with 403s/timeouts.
• Keep the original reader-facing links instead of replacing live resources with archived copies.

Test plan

• ruby -ne 'next if $_.strip.empty? || $_.start_with?(\"#\"); Regexp.new($_.strip)' .lycheeignore
• Verified every failed Actions URL matches a .lycheeignore regex.
• git diff --check