List ChatGPT Ads pixels

Lists the measurement pixels on the advertiser account, when each last received an event, and whether a Conversions API key exists for it. The key itself is never read or shown — only whether one is there. Use when: the user asks about conversion tracking, or before launching anything with a conversions objective, because that objective needs a conversion event to optimise towards. Do not use it to read results — conversions that were recorded show up in chatgpt_get_performance. Do not tell the user tracking "works" because a pixel exists: a pixel that has never fired is not tracking anything, which is what the last-event column is for. Returns one row per pixel. Pixel management has to be enabled on the ad account; when it is not, the platform answers 404 and the tool says so explicitly instead of failing — that answer is final, so relay it and move on rather than retrying. The platform publishes how to create a pixel but not how to list them, so treat an empty result as "nothing visible to the API", not as proof that nothing exists.