subsidy is a chain KPI, not a bench

[Flotapponnier]

Summary

• Kills benchmarks/robinhood-subsidy.yml. Reason: it had no real 'providers' cohort, the 3 rows were just KPIs of a single chain, and /products/countdown, /products/chainside-cost, /products/projection were nonsense pages
• Harness stays untouched: metrics keep flowing to Prom (robinhood_subsidy_days_remaining, robinhood_subsidy_chainside_cost_total_usd, robinhood_subsidy_projected_total_usd)
• Extends ChainKpis + the strip renderer with 3 subsidy cards, gated on slug === "robinhood" so every other chain skips them silently. Days card uses a fmtDays formatter ("77d"), USD cards reuse fmtUSD