Show federal vs. state fiscal impact in budget view

[MaxGhenis]

Context

PolicyEngine-US and policyengine-api are adding federal vs. state fiscal impact attribution (see PolicyEngine/policyengine-us#8075, #8076). The app does not currently show a federal/state split in budget impact views.

Proposed change

On the budget/fiscal-impact section of the reform output:

1. Add a stacked bar (or two side-by-side bars) showing federal vs. state fiscal impact of the reform, alongside the existing total.
2. Detailed budget table: add columns for "federal" and "state" next to the existing "difference" column, so per-program attribution is visible (the existing detailed_budgetary_impact keyed by program becomes a matrix of program × level-of-government).
3. Copy update on the fiscal impact narrative: current phrasing conflates "federal fiscal impact" with total cost. Distinguish once the API exposes the split.

Dependency

Blocked by policyengine-api change to expose federal_budgetary_impact and state_budgetary_impact (separate issue). Variables already exist in policyengine-us post-#8076: federal_benefit_cost, state_benefit_cost, and per-program medicaid_federal_cost / medicaid_state_cost / chip_federal_cost / chip_state_cost.

Why this matters

For reforms that shift cost between levels of government (Medicaid expansion rollback, OBBBA SNAP state match, FMAP changes), the fiscal story is federal-vs-state, not aggregate. Users currently can't see this from the app.

Related

• Add federal vs. state cost attribution for benefit programs (Medicaid FMAP, SNAP OBBBA, CHIP eFMAP, etc.) policyengine-us#8075 (scoping)
• Add Medicaid + CHIP federal/state cost attribution via FMAP policyengine-us#8076 (Medicaid + CHIP attribution)
• policyengine-api issue for the API surface