Calibration reconciler

Walks fix branches to falsify the gating-verdicts that should have caught the bug, computes per-skill Brier calibration scores, and writes a falsification log to the central ledger ~/.claude/crucible/ledger/ (override CRUCIBLE_LEDGER_DIR). The SKILL.md is a thin prompt wrapper; the source of truth is the testable Python core at scripts/reconcile_ledger.py.

Skill type: Utility — direct execution, no subagent dispatch.