Add product listing repeat evidence

[sjh9714]

Summary

• Add clean product-listing repeat3 k6 evidence and metadata.
• Separate the historical README p95 record from the current local remeasurement snapshot.
• Update performance docs and k6 evidence wrapper notes.

Test Plan

• BASE_URL=http://localhost:5001 k6/run-with-evidence.sh product-listing
• bash -n k6/run-with-evidence.sh
• k6/run-with-evidence.sh --help
• ./gradlew test
• ./gradlew build

Notes

• Raw console.txt preserves k6 output exactly; git diff --cached --check flagged trailing whitespace in that raw artifact.