Rank LinkedIn creatives (ads) and flag fatigue

Ranks the creatives (ads in Campaign Manager) of one campaign (ad set) against each other on CTR and cost per lead, and flags the ones whose CTR fell sharply in the second half of the window — the signature of creative fatigue on LinkedIn's small, repeatedly-reached audiences. Use when: deciding which ad to keep, which to refresh, and which to leave alone. It is the read to run before linkedin_pause_creative. Do not act on a creative marked "too_early": under 1,000 impressions the numbers are noise, and pausing it destroys the test. Do not treat fatigue as a reason to cut spend — on LinkedIn it means the same people have seen the ad too often, and a new creative into the same audience is usually the fix. Do not use it to compare campaigns; that is linkedin_get_campaign_performance. Returns a verdict per creative (winner / steady / underperforming / fatiguing / too_early) with the number behind it, plus the campaign average it was judged against. If every creative is "too_early", say the campaign needs more time and recommend nothing.