refactor: remove vendored binaries and raw assets from repo

scripts/purge-git-history.sh

@@ -0,0 +1,14 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+cat <<'EOF'
+This rewrites git history to remove large vendored assets.
+Run only after committing the current tree cleanup and coordinating with collaborators.
+
+Commands:
+  git filter-repo --path dcmtk-bin --path legacy/raw --invert-paths
+  git push --force --all
+  git push --force --tags
+
+Afterward, collaborators should reclone or hard-reset to the rewritten history.
+EOF