Investigate: show hours-worked LSR charts alongside earnings charts (UK)

Context

Tracking issue from PolicyEngine/policyengine-uk#856.

The US app surfaces hours-worked charts alongside the earnings / budgetary-impact charts for labor supply response (LSR) reforms. The UK app currently only shows the earnings-side view.

Model state (UK)

The UK model already exposes the underlying variables — this is not a country-package gap:

• hours_worked (input, annual)
• weekly_hours (derived)
• benunit_weekly_hours (aggregated)
• employment_income_behavioral_response (LSR income delta)

An hours-equivalent response is a derived quantity from the income delta and the wage rate; it can be computed at the API/app layer without model changes, or optionally exposed as a dedicated variable (hours_behavioral_response) in policyengine-uk.

Ask

Investigate whether to:

1. Port the US hours-worked chart component to the UK LSR results view, computing the hours delta from existing outputs, or
2. Request a new hours_behavioral_response output variable from policyengine-uk and wire it through the API.

Option 1 keeps the work in the frontend; option 2 makes the output first-class but requires a country-package release.

Start by locating the US hours-worked chart component and the UK LSR results view, then compare how the existing earnings outputs reach the app. Determine whether the hours delta can use current outputs or requires a new policyengine-uk variable; done means a documented implementation path and agreed option.