Add the high value council tax surcharge

[MaxGhenis]

Summary

• add the England-only high value council tax surcharge from April 2028 using the November 2025 Autumn Budget bands
• evaluate properties against the 2026-price thresholds by deflating main_residence_value with the same per-capita-GDP index used to uprate the input
• flow the surcharge into household and government tax aggregates and cover the start date, CPI uprating, and England-only scope with regression tests

Testing

• uvx ruff check policyengine_uk/variables/gov/hmrc/high_value_council_tax_surcharge.py policyengine_uk/tests/test_high_value_council_tax_surcharge.py
• uv run --python 3.13 pytest -q policyengine_uk/tests/test_high_value_council_tax_surcharge.py

Closes #1392.