Preflight: which PT number types can be purchased right now

Returns the current Telnyx requirement-group status for each PT number type. Used by the purchase dialog to disable types whose group isn't 'approved' so users see the situation upfront instead of failing at checkout.

Cached in Redis for 10 minutes (status changes are rare; admin fix propagates within that window).

Response shape: { "local": {"status": "approved", "can_purchase": true, "group_id": "..."}, "national": {"status": "expired", "can_purchase": false, "group_id": "..."} }