Modernize Processing sketches and add ribbon and field shaders

[daitomanabe]

Summary

• Modernize the original point-skeleton sketch using retained PShape geometry, PVector, typed collections, and explicit playback state.
• Add Motion Ribbons (cached joint trails, triangle strips, vertex + fragment shaders) and Motion Field (joint uniforms and a full-screen fragment shader).
• Keep all BVH data in its original location; the sketches share it and include identical small parser JARs for direct PDE execution.
• Add actual rendered previews, short teaching guides, bounded render checks, and CI screenshot/log artifacts.
• License only the new code under MIT; preserve the original parser/data copyright status and historical credits.

Verification

• All three sketches compile and render with official Processing 4.5.6 on macOS.
• Two motion timestamps produce nonempty, different images; shader program linkage is checked explicitly.
• Missing and malformed shaders fail without a success marker.
• Maven parser tests pass; all parser JAR copies and regenerated API documentation match.
• Workflow lint, staged diff checks, and local-path/privacy checks pass.

Processing's standard PShader exposes vertex and fragment stages. The ribbon topology is generated in the sketch; no geometry-shader extension is required.