metrics: refresh leaderboard, backtest, statpack, scope

[fedcourtsai-dev]

Scheduled metrics refresh: the committed artifacts drifted from their inputs (the data/ evaluations ledger and the corpus), so the scheduled refresh regenerated them with the same tested fedcourts commands the pipeline runs. Deterministic — an unchanged input produces a byte-identical artifact, so only genuinely stale files appear here.

artifact	now holds
metrics/leaderboard.json	[frozen] 0 predictor(s) ranked from 0 evaluation(s) (0 forward / 0 retrospective / 0 procedural)
metrics/backtest.json	2 predictor(s) over 16269 resolved event(s) (retrospective by construction)
metrics/statpack.json	2151683 corpus case(s): 40274 resolved / 2111409 open
metrics/statpack.md	human-readable statpack companion
data/scope/scope.json	3102 public case(s): 3102 eligible / 723 excluded

Refresh run 30731126724. Review and merge — this PR is intentionally not auto-merged; if it sits unmerged, the next scheduled refresh force-pushes this same branch and the PR updates in place.