fix(subscriptions): enforce 2023/2024 as first FY, apply 50% discount, full rewrite

- Remove unpaid subscriptions before 2023/2024 (system didn't exist)
- Apply 50% discount to all 2023/2024 subscriptions
- Fix amounts/discounts for all years based on historical rate table
- Reset and recalculate all fines from scratch
- Delete orphaned subscription rows with no matching dependent
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>