Why:
- ADR-0001's Qdrant payload records embedding_model_version so a future model
swap can identify which chunks need re-embedding. The embedder is what
knows which model produced its vectors, so it reports this rather than the
call site reconstructing it from settings.
Changes:
- DenseEmbedder/SparseEmbedder protocols gain a model_version: str attribute.
- OpenAICompatibleEmbedder reports its configured model; Bm25SparseEmbedder
reports its analyzer (bm25-<analyzer>).