Check Eligibility

Check whether the user can reserve a demo number.

Eligibility rules (must all be true):

• User has NOT used their demo before
• User has NOT made a paid topup (paid users buy real numbers)
• No active reservation currently

Note: "has paid" users can still reserve, but they're encouraged to buy. We don't block them — they can demo if they choose. But UI shows "Buy Number" as primary for paid users.