Vector acceptance benchmarks and budgets (VV7) #329

Part of epic #305.

Problem. The only vector numbers are documented microbenchmarks at 10K vectors (docs/content/docs/guides/indexing.mdx:10-17, BENCHMARKS.md:157-166); nothing measures maintained similarity views, and vectors and indexes are not metered (/metrics memory = tuples x 64).

Target. A perf-gate vectors scenario on the benchmark host (1M x 384-dim random normalized vectors, 10,000 query keys): B17-B23; memory accounting of vector store and index bytes per KG under V15's budget; recall gate against brute force in CI (small) and on the host (1M).

Acceptance. B17-B23 pass; make bench-vectors-remote records nproc, commit, command; metrics vector_bytes, index_bytes, index_epoch per KG.

Size M. Dependencies V15, VV5. Order slot 9.