[nicobatberger-design]

Summary

Adds an offline converter for SketchUp SKP files and ZIPs containing one SKP so users can convert models to GLB for local inspection without uploading the model to an online service.

Related issue

N/A

Changes

• Add conversion of SKP and single-SKP ZIP inputs, preserving component instances and writing scene metadata alongside the GLB.
• Reject unsupported inputs and unsafe or ambiguous ZIP contents; add focused usage documentation and tests.

Testing

• python -m pytest -q tests/tools/test_skp_to_glb.py - passed (4 tests).

Checklist

• The change is focused on a single logical concern.
• I ran the relevant tests locally (make test-contracts / make test) where applicable.
• I updated docs/README if behavior or usage changed.
• No unrelated files (build artifacts, local config) are included in the diff.