Testing checklist: Ubuntu 26.04, WSL1, act/GHA, and minimal per-language setup steps

[darkn3rd]

Testing checklist

• Test the full lesson suite on Ubuntu 26.04 (native, not WSL)
• Test the full lesson suite on WSL1 (Ubuntu) - distinct from the
  WSL2 instance already used for Docker/act
• Test with act (local GitHub Actions runner) on Ubuntu, to
  validate .github/workflows/ci.yml behaves the same locally as it
  does on real GitHub-hosted runners
• For each area above, document the minimal install steps per
  language/toolchain (e.g. for C++, is g++ alone sufficient, or does
  something else need to come with it?) - same spirit as the
  base-devel/Devel-category minimal-package findings already worked
  out for MSYS2/Cygwin earlier