Add lightweight concept metadata API and release packaging
Add ConceptMetadata for metadata-only access without neural imports or model-weight downloads. Expose the same implementation through model.metadata, retain existing explain/get_prevalence behavior, and provide exact threshold/bound lookup, fidelity access, DataFrame export, and metadata save/reload.
Update the standalone runtime and installation instructions, include metadata-only requirements and a fresh CPU smoke-test report, and regenerate checksums. Exclude historical training records and verification/example artifacts from the release.
Validation: 14 tests passed. The staged standalone release passed real CPU text inference, exact agreement between combined and separate encoding stages, complete metadata alignment, and metadata-only save/reload with neural imports blocked. Encoder/embedder weights, concept labels, and saved statistical arrays are unchanged.