fix(self-improve): totalCostUsd excludes both held-out gate arms

[drewstone]

selfImprove.totalCostUsd reports only part of what the loop spends: both held-out gate arms are excluded.

Measured on a smoke: reported $0.051 vs $0.093 actually spent — the difference equals the two holdout arms to 4 decimal places.
Confirmed on the first live campaign (agent-runtime-swe commit 3b93916c): loop-provenance totalCostUsd = $1.3305 vs $1.667 summed across all 660 cells in cells.jsonl; the $0.336 gap matches the two 60-cell holdout arms.

Cost accounting should include everything the loop spends, holdout gate included — anyone budgeting off totalCostUsd underestimates real spend by ~20-45%.