feat(backfill): populate duration_seconds and tokens-per-second on historical runs

feat: publish 12 benchmark runs (local sweep 2026-04-19)

feat: rescue 12 older orphan benchmark files (12 rows from 2026-03-23 and 2026-03-30 runs)

feat: rescue 26 orphan F8 sweep files (91 rows, 13 models x 2 suites)

test(scaffold-poc): remove after successful gating verification

test(scaffold-poc): verify HfApi append pattern with unique filename

feat: initial import of 140 benchmark rows from 56 historical runs