UK reform contract: wrapper.household errors under the candidate script, so every UK candidate is rejected #645

Every automatic UK candidate is rejected by the reform_contract gate because every wrapper.household row errors with:

AttributeError: 'NoneType' object has no attribute 'calculate_household'

Cause. scripts/check_uk_candidate.py sets POLICYENGINE_SKIP_COUNTRY_IMPORTS=1 at startup (line 43). With that flag, policyengine/__init__.py binds policyengine.uk = None. The contract's _WrapperHouseholdRoute._call then reaches the wrapper as pe.uk.calculate_household(...), so each household case errors before it runs. The country routes import policyengine_uk directly and are unaffected.

Evidence. Candidate 2.134.5-1.58.2 (pair 996a156c…, #639) was rejected with "16 contract row(s) failed". In the published gates/reform_contract.json, 15 are error rows and 1 is a fail row (unknown_path's rejection check, whose actual error is the same AttributeError), all on wrapper.household. Candidate 2.134.6-1.58.2 (#644) is qualifying on the same code.

Effect. No UK candidate can reach qualified or needs_review through certify-uk-release, so automatic promotion cannot pick up the pe-uk releases due before the 28 October Budget.

Fix. Import policyengine.tax_benefit_models.uk in the route. It exposes the same calculate_household function and does not depend on the skip flag. Add a regression test that runs the route in a subprocess with the flag set.