docs(sbom): map example evidence types

[stacknil]

Summary

• add an artifact evidence map to the SBOM reviewer path
• distinguish deterministic no-network examples, mocked enrichment snapshots, and consumer workflow templates
• clarify that provenance and Scorecard samples demonstrate rendering/policy semantics, not live package truth

Validation

• git diff --check
• python scripts/regenerate-example-artifacts.py --check
• python -m pytest tests/test_example_artifacts.py tests/test_provenance_reporting.py tests/test_scorecard_reporting.py
• checked referenced local paths exist

Privacy / security

• checked changed docs for local paths, school identifiers, and secret-like strings