iblai-api-external-service-proxy は何をしますか？
Call third-party AI services through ibl.ai's External Service Proxy — a platform-admin gateway that fronts ElevenLabs (TTS, voice management, dubbing, sound generation, audio isolation, history/quota) and HeyGen (avatar & template video, translation, photo avatars, assets, voices, quota, webhooks). Discover the available services and their endpoints, then POST a request envelope (body/query/headers/path_params, plus multipart files) to invoke one action — the provider API key is stored server-s