Check chat card copy and image before building an ad

Checks a chat card against the rules before anything is created: the headline is 3–50 characters, the body at most 100, the destination an https URL of at most 2048 characters, and the image square, at least 400 px a side, under 10 MB and one of image/jpeg, image/png, image/webp. Use when: you have drafted copy, or the user pasted copy or an image URL, always before chatgpt_create_ad or chatgpt_launch_ad. Call it with no arguments at all to get the limits themselves. Do not use it for policy questions — it checks lengths, formats and reachability, never whether the claim in the copy is allowed. Do not use it to check a live ad: read that with chatgpt_list_ads. Returns every problem at once, split into things that will be refused and advice. Fix the refusals before creating anything; the writers apply exactly these rules and will refuse the whole call otherwise. Calls no ad platform, needs no connection and costs nothing, so run it as often as it helps. If the copy is too long, say so and ask the user how to shorten it — never rewrite their wording to fit.