Document MS MARCO 1M SQLite reuse result

[SonAIengine]

Summary

• document the local persistent MS MARCO 1M SQLite DB build
• record the reuse-mode rerun that skips the ingest/index phase
• note the gitignored DB and sidecar artifact sizes

Results

• persistent build: 1,000,000 docs, 50 queries, MRR@10 0.462, Hit@10 30/50, build 2184.3s, search 71.0s
• persistent reuse: 1,000,000 docs, 50 queries, MRR@10 0.462, Hit@10 30/50, build 0.0s, search 70.1s
• local artifacts: tests/benchmark/data/msmarco_1m.db (1.2 GB), tests/benchmark/data/msmarco_1m.db.tier1.json (535 bytes)

Checks

• git diff --check
• inspected updated markdown section

No code changes in this PR.