refactor: remove vendored binaries and raw assets from repo

docs/repo-size-cleanup.md

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+# Repo size cleanup
+
+Implemented in the working tree:
+- removed tracked binaries from `dcmtk-bin/`
+- removed tracked raw assets from `legacy/raw/`
+- added `.gitignore` protections
+- added setup scripts for DCMTK and MicroDicom
+
+## Finish the cleanup in git history
+Rewriting history is still required to shrink the remote repository size.
+
+```bash
+git filter-repo --path dcmtk-bin --path legacy/raw --invert-paths
+git push --force --all
+git push --force --tags
+```
+
+Coordinate this with any collaborators first.