Adds SubscriptionDataMigration service that:
- Fixes orphaned person_id references (matched wrong ID to dependent)
- Removes exact duplicate subscription rows
- Corrects zero/wrong amounts using historical rate table
- Creates missing subscriptions for all members from join date to present
- Applies overdue fines proportionally per SubscriptionCalculator rules

CLI commands:
  php cli.php subscriptions:migrate          Run the migration
  php cli.php subscriptions:migrate --dry-run Preview changes
  php cli.php subscriptions:validate         Check data integrity
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>