feat(tools/subversion): Apache Subversion (SVN) support — ASF svn.apache.org / dist.apache.org

[potiuk]

Add tools/subversion/ for Apache Subversion (SVN) support. This one is directly relevant to the ASF itself: svn.apache.org still hosts active source trees for a number of TLPs, and dist.apache.org (the release-distribution area every ASF release is staged and published through) is SVN, not Git. A framework that stewards ASF project workflows but can't touch SVN is blind to a core piece of ASF release infrastructure.

Capabilities to provide:

• Checkout / update / svn diff / svn status against a working copy
• History read: svn log, svn blame, file-at-revision
• Commit with message (write-path gated on explicit user confirmation in the calling skill)
• dist.apache.org-aware helpers: stage/promote release artefacts under the SVN release area (useful for a future release-management skill family)
• Reuse the VCS-capability shim introduced by tools/mercurial/

Why: Beyond ASF infra, SVN remains in heavy use across enterprise, legacy OSS, SourceForge-hosted SVN repos, and large monorepos that never migrated. For ASF adopters specifically, dist.apache.org support is not optional — it is how releases ship.

Reference:

• SVN book: https://svnbook.red-bean.com/
• ASF dist area: https://dist.apache.org/repos/dist/
• Depends on the VCS abstraction from the Mercurial bridge issue