Enable Plan Changes When Restarting an Expired Membership

🔍 Problem Statement
As a Pelcro admin, I experience the restart-expired-membership flow restricting plan selection to the original plan only, which forces customers to cancel-and-resubscribe if they want a different plan and causes unnecessary churn.

💡 User Story
As an admin, I want to select any active plan when restarting an expired membership, so that customers can upgrade, downgrade, or switch without losing their history.

🎯 Definition of Done
- Given an expired membership, when an admin initiates the restart flow, then a plan selector is shown allowing any active plan.
- This change impacts the UI (restart membership modal) and API (subscription restart endpoint).
- Limitations: same proration rules apply as mid-cycle plan changes.

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Problem Statement Currently, when restarting an expired membership, admins are restricted to the original plan and cannot select a different one. This limits flexibility and creates friction, especially for customers who want to upgrade, downgrade, or switch plans based on their current needs. As a result, users may abandon the restart flow or require manual intervention. User Story As an admin restarting an expired membership, I want to be able to select a different plan during the restart process, so that I can choose a plan that better fits my current needs without extra steps or support involvement.