Abolish income-related ESA from 1 July 2026 (NI 1 October 2026) and stop paying it alongside UC

Problem

Two related problems with income-related ESA:

The abolition is not modelled. SI 2026/409 (made 15 April 2026) inserted art 3A into SI 2025/1148, so the ESA "amending provisions" come into force on 1 July 2026 for the remaining old-style ESA awards. That ends income-related ESA.
- Art 3A(2) saves awards where a person is appointed under reg 57 of the Claims and Payments Regulations 2013, or where an appointee was judged likely to be needed within the previous 6 months.
- Northern Ireland has the same structure from 1 October 2026 (SR 2025/176 art 3A, inserted by SR 2026/115).
esa_income passes reported awards through a capital screen with no end date.
ESA(IR) and UC overlap. esa_income is not gated on the UC claim and is not UC unearned income. On the Enhanced FRS 2024-25 (uk-data 1.56.16, main at 1c5b4d0, 2027), the model pays £2.23bn of ESA(IR) to 188.8k benefit units. £1.64bn of it goes to 137.8k units that also receive UC. A UC claim ends an old-style ESA award.

Reuse the pattern from Abolish working-age Housing Benefit from 1 July 2026 (NI 1 October 2026) #1910 for the working-age HB abolition: a numeric 1/0 parameter per jurisdiction with fiscal_year_blend: true. A bool is sampled at 30 April and would leave 2026-27 unaffected.
Zero esa_income for benefit units that claim UC.
Check UC Regs 2013 reg 66(1)(b) on whether contributory (new-style) ESA should be added to the UC unearned-income list, which already has jsa_contrib.
Hand-checked YAML tests; property tests for "no benefit unit receives both ESA(IR) and UC" and "ESA(IR) is zero after the abolition"; a real Enhanced FRS impact.
This should land before Move working-age legacy-benefit reporters onto UC at Move to UC claim rates (stranded after HB, tax credit, IS and JSA closure) policyengine-uk-data#492. That issue moves more ESA(IR) reporters onto UC, which would widen the overlap.