Purchase Confirmation Menu

After choosing a subscription, show a confirmation dialog with info and "Confirm"/"Cancel" buttons.

📋 Acceptance Criteria

• GIVEN the user selects a subscription

• WHEN the confirmation popup appears

• THEN it displays plan info and confirm/cancel options

• GIVEN the user confirms

• WHEN they press the button

• THEN the purchase is completed and success screen appears

✅ Please check the Definition of Done before moving this issue to Close.