GET /v1/voices now returns a pagination-ready envelope

GET /v1/voices now returns an object envelope instead of a bare array. The new response has a voices field plus pagination metadata, which gives the API room to grow without another shape break later.

Before this change, clients read the response body directly as an array. After this change, clients should read response.voices and use the pagination fields when they need to walk the catalog.

This is covered in the Build changelog. If you use an official SDK, update to a generated version that matches your pinned Speechify-Version date.