Make pgvector and the model registry schema-aware; fix sqlite-vec's engine reconstruction

[nicoloesch]

Depends on AustralianCancerDataNetwork/omop-alchemy#57. Requires pyproject.toml version update for oa-configurator, orm-loader, and omop-alchemy

Summary

What changed

-table_exists, index management, and model-registry lookups all ignored the connection's configured schema, so a non-default-schema pgvector deployment silently read/wrote the wrong tables.

• Fixed via oa-configurator's schema-aware primitives, with new non-default-schema regression coverage.

• create_sqlitevec_engine() no longer rebuilds its own engine from a bare path

  • it now wraps an already-resolved Engine directly.

• The model registry now lives in its own reserved schema (MODEL_REGISTRY_SCHEMA), independent of whichever schema the embedding store itself resolves to

Removed

• PGVectorEmbeddingBackend.from_db_url() (dead code, zero callers).

Checklist

• Applied exactly one label (breaking, feature, fix, dependencies, or chore)
• Tests pass locally (uv run pytest -q): 151 passed, 5 pre-existing unrelated failures