Decide the fate of open-questions.md and experimental-findings.md #130

Both docs/open-questions.md and docs/experimental-findings.md carry a "not actively maintained" banner, yet findings PRs (#95, #112, #116) still land in the latter and issues still route work into both.

Either lift the banner and keep them current (the findings template from #112 helps), or freeze them as historical snapshots and point contributions elsewhere.