Agent Skills: cost-impact

Compute a Claude Code cost-impact report across a time window, grouped by repo with per-session detail. Prices per-turn per-model at published list rates (Fable 5 / Opus 5 & 4.x / Sonnet 4.x-5 / Haiku), includes subagent tokens, outputs markdown with clickable PR links and collapsible per-repo sections. Use when user asks "how much did I spend on Claude this week", "cost report", "/cost-impact", or wants a weekly retrospective on Claude usage.