Archive the legacy SVN tree #112

Follow-up to #111. The DOAP source was switched to the document generated by the current website in this Comdev change, but the broader SVN tree still needs a clear archival status.

The SVN tree contains trunk/, branches/, tags/, site/, and steve-web/. Its last change was in March 2021 (r1887525); the old DOAP file dates from June 2014 (r1602421). Active development and website sources now live in this Git repository, with project metadata maintained in .asf.yaml.

Proposal: retain SVN as a read-only historical archive, with clear links to the maintained sources.

• Check remaining builds, scripts, and public references for SVN dependencies, and confirm that projects.apache.org has regenerated its STeVe entry from the new DOAP URL. Identify any SVN-only material that still needs active maintenance.
• Record project consensus on dev@steve.apache.org for archiving the entire /steve/ SVN tree.
• Add a migration README at the SVN root and notices at relevant legacy entry points, linking to this repository, https://steve.apache.org/, and the generated DOAP.
• Ask Infra to confirm or set /steve/ read-only, following the SVN-to-Git guidance. Preserve the existing URLs and revision history; no ongoing Git-to-SVN mirroring is proposed.

Done when SVN is clearly marked as historical and read-only, and active builds and project metadata no longer depend on its contents.