- Migration: retroactively applies 50% discount to all unpaid 2023/2024
  subscription rows (discount on gross total = base + dev fee)
- SubscriptionGenerator: year-specific discount now applied on per-row total
  (base + dev_fee) and stored in discount_amount column, not just on base rate

Business rule: SUBSCRIPTION_YEAR_ADJUSTMENT_2023 mandates 50% reduction on
the final subscription total for all person types in that fiscal year.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>