Modernize example for Processing 4.5.6

[daitomanabe]

Summary

• update the sketch and bundled BVH parser for Processing 4.5.6 / Java 17
• add reproducible Maven builds, parser regression tests, current API documentation, and pinned GitHub Actions CI
• document project stewardship and preserve the original authorship history
• keep the three original BVH data files unchanged

Verification

• mvn --batch-mode --no-transfer-progress clean verify javadoc:javadoc (4 tests)
• generated JAR and Javadocs exactly match the committed artifacts
• official Processing 4.5.6 CLI build
• ten-frame P3D runtime smoke test with all three motions
• old/new pose output compared bit-for-bit at representative frames; no public API removals
• workflow validated with actionlint; Action SHAs and official Processing asset checksum verified

License note

The original repository has no license file. This PR does not infer or add one; README now states the current status. Issue #1 therefore remains an owner/rightsholder decision.