Add quality-focused gRPC benchmark sweep

[SaiSandeepKantareddy]

Summary

• add a reusable gRPC quality sweep runner for staged benchmark work
• document a quality-first benchmark methodology
• add a retrieval/vector benchmark plan note to focus new work
• add a server-side embedding bakeoff runner for model-vs-model quality comparisons

Why

This gives us a repeatable way to compare HNSW profiles on the same dataset and embeddings, and then compare stronger embedding models on the same evaluation path. That is the right order before considering alternative ANN families.

Validation

• bash -n scripts/run_sochdb_grpc_quality_sweep.sh
• bash -n scripts/run_sochdb_embedding_bakeoff.sh
• ran the first SciFact HNSW quality sweep on the benchmark server successfully
• started the first server-side embedding bakeoff run