Start dates and current active subscriptions

For GiveCampus reporting.

For parent subscription rows, subscription_start_date uses the explicit recurring start date when present, otherwise the subscription creation time. For installment rows, installment_subscription_start_date refers back to the associated subscription. A billing start date can differ from setup/creation, especially for future starts; choose the field that matches the reconciliation question.

A current active-subscription count needs the full relevant creation range, not only the current fiscal year. Include current subscription state, end date and remaining-charge fields, and count distinct subscription IDs. The model's active scope checks state, future end date and remaining charges; a state label by itself is not the entire eligibility definition. A historical as-of count requires historical evidence rather than today's state.