Update remaining OBR forecasts to March 2026 detailed tables

[MaxGhenis]

Summary

Updates the remaining OBR economic forecast parameters from November 2025 to March 2026 EFO detailed forecast tables. This is a follow-up to PR #1512 which updated the main Table A.1 variables but awaited publication of the detailed tables for the remaining variables.

Variables updated

Variable	Source table	Key changes
CPIH	Economy Table 1.7	2026: 2.67% → 2.55%
CPI AHC	Derived from CPI/rent	2026: 1.7% → 1.58%, added 2030
Non-labour income	Economy Table 1.12	2025: 5.19% → 3.49%, profile reshaped
Per capita mixed income	Table 1.12 − population	2025: 0.24% → 0.69%
Per capita non-labour income	Table 1.12 − population	2025: 4.47% → 2.75%
Council tax England	Expenditure Table 4.1	2025: 7.81% → 7.02%
Council tax Wales	Expenditure Table 4.1	2025-30: 5.81% → 7.43-7.73%
Council tax Scotland	Expenditure Table 4.1	Unchanged (0.0384)
Mortgage interest	Economy Table 1.7	2025: 10.98% → 9.52%, 2030 kept
Rent	Economy Table 1.7	Minor adjustments
Household interest income	Table 1.12 (proxy)	Follows non-labour income

All reference metadata updated from "November 2025" to "March 2026" with correct table citations.

Data sources

• OBR EFO March 2026 — Economy detailed tables
• OBR EFO March 2026 — Expenditure detailed tables

Test plan

• CI tests pass (some test expected values may need updating)
• Verify values match OBR published tables

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