[CHORE] Retain raw benchmark artifacts for 90 days

[lukekarrys]

Context

The workflow currently uploads results-*, version data, and processed results with retention-days: 7. Raw artifacts are the only source for reprocess.yml and request-log forensics, both of which were needed during the registry performance incident.

Seven days leaves very little time to detect, investigate, and correct a historical data problem. The findings recommend 90 days; expected storage cost is small relative to the debugging value.

Acceptance criteria

• Relevant benchmark result uploads use retention-days: 90.
• reprocess.yml documentation/UI reflects the available reprocessing window.
• The retained set includes the raw per-matrix files needed to audit exit codes and request logs.
• Any intentionally short-lived or redundant artifact is called out separately.

Source

Performance investigation: item 8 — artifact retention