test(recall): add live memd producer for recall benchmark

[sun-970]

Summary

• Add a producer that queries a running memd via POST /v1/search over every dataset query and emits a mem.recall-rankings.v1 file, closing the gap where the recall benchmark had a measurement harness but no way to produce rankings from the search path that actually ships.
• New produce subcommand on python -m benchmarks.recall with --memd-url, --token, --dimension, --mode, --provider, --model flags.
• Maps API results back to dataset doc_ids by matching the path field, with snippet overlap for disambiguation when multiple documents share a path.

Changes

• benchmarks/recall/live_producer.py: producer module — queries memd, records client-side latency, maps results to dataset doc_ids
• benchmarks/recall/__main__.py: add produce subcommand
• benchmarks/recall/tests/test_live_producer.py: unit tests for path index, snippet matching, success and error paths
• benchmarks/recall/README.md: document the live producer recipe and filter translation

Usage

# Produce rankings from a live memd
python3 -m benchmarks.recall produce \
  --memd-url http://localhost:8080 \
  --token "$MEM_TOKEN" \
  --output /tmp/live-rankings.json \
  --dimension 1536 \
  --mode hybrid

# Score against the lexical baseline
python3 -m benchmarks.recall run \
  --rankings /tmp/live-rankings.json \
  --output /tmp/live-artifact.json \
  --compare benchmarks/recall/baselines/lexical-reference.v1.json

Test plan

• All 33 existing recall benchmark tests pass
• 5 new unit tests for the producer (path index, snippet matching, success, error)
• Maintainer verifies against a live memd instance with the benchmark corpus loaded

Fixes #175

[PeterGuy326]

HOLD — the five producer unit tests pass locally on current head 89bb12bdf2ae5edbdfa17260953ec6352ab9239f, but the PR explicitly leaves the live memd acceptance unchecked and no CI is reported. Please run the producer against a real memd with the benchmark corpus loaded, attach the generated ranking artifact/command output, and trigger exact-head CI.

[PeterGuy326]

Current-head CI approval readback (2026-09-10)

Head: 89bb12bdf2ae5edbdfa17260953ec6352ab9239f. The original pending-approval runs on this head have been approved and real check-runs now exist (17 at this snapshot). No old-head run was approved. Auto-merge remains disabled; this is not a code approval or merge-ready declaration.

• PR Policy / 34191624178 — attempt 2, completed / success
• ByteFolk Security Baseline / 34191624050 — attempt 2, completed / success
• Validate Agent memory / 34191624005 — attempt 2, completed / success
• CI / 34191623985 — attempt 2, completed / failure

Failures at this snapshot:

• Web

[sun-970]

Superseded by @PeterGuy326's #196 which covers the same changes on current main. Closing per the '本轮先不合并' directive.