Fetch contacts

Fetch contact emails for a search filter or by specific adapt IDs. Requires authentication via Bearer token or API key in query parameter (?api_key=... for /api/v1/). Either provide id (array of adapt IDs) with filter_id, or limit with filter_id to fetch up to limit contacts for that filter. Limit and credit checks apply when using limit; failures return 200 with success: false and an error message.