List the caller's reusable studio voices.

Lists the studio voices owned by the caller: designed voices (text-description voice design) and cloned voices (recorded sample, sourceKind: "cloned"), each with the provider that speaks it. Each entry carries { voiceId, name, provider, sourceKind, isCloned, retiresAt, retired, consent } and what uses it (usedBy, useCount, inUse, usedByLine); the voices something uses come first, and the rest (inUse: false) are the Voices library's "Not used" group. Assign one to a character via the cast/voice surfaces using voiceId + provider. A voice with retiresAt is on a provider that is shutting its voices down: migrate it before then (POST /voice-migrations); once retired, it can no longer speak. A cloned voice speaks only while consent.status is recorded: one with required needs its subject to confirm (POST /voices/{voiceId}/consent-link), and one with revoked can never be used again. Scope: story:read.