Allow auto renew gifts

🔍 Problem Statement

As a publisher or operations admin using Pelcro,

I experience that all gift subscriptions are treated as one-time purchases, regardless of the plan’s renewal configuration,

which results in inability to offer auto-renewing gift subscriptions and inconsistent renewal behavior compared to standard subscriptions.

💡 User Story

As a publisher or subscription admin,

I want gift subscriptions to inherit their renewal behavior from the selected pricing plan,

so that one-time and auto-renewing gift subscriptions are supported natively and behave predictably.

🎯 Definition of Done (DoD)

A feature is done when:

✔ Given a pricing plan with renewal_type = self-renew, (NOTHING CHANGES)

when a gift subscription is created using this plan,

then the gift subscription remains one-time and does not auto-renew, matching current behavior.

✔ Given a pricing plan with renewal_type = auto-renew,

when a gift subscription is created using this plan,

then the gift subscription auto-renews according to the plan’s billing cycle using Pelcro’s standard renewal and dunning logic.

✔ This change will impact API, specifically subscription creation and renewal logic for gift subscriptions in the backend.

✔ This solution will include the following limitations:

1. Existing one-time gift subscriptions are not retroactively converted to auto-renewing

2. Renewal behavior is determined only at subscription creation time

3. No UI changes are included as part of this feature

4. No mixed renewal behavior within a single gift subscription is supported