Create custom audience

Create a custom audience. customer_list is supported on Meta, Google, X, LinkedIn, TikTok, and Pinterest; website and lookalike are Meta-only. saved_targeting stores a reusable TargetingSpec (no member upload, no adAccountId) that you reference later via savedTargetingId on POST /v1/ads/create. Upload-backed audiences are created empty, add members via POST /v1/ads/audiences/{audienceId}/users. On TikTok and Pinterest the audience is provisioned lazily on the first member upload (until then its status is pending). Create is not idempotent, never auto-retry.