Hitting audience targets

When a brief has targets, such as "at least 7% core audience and 100,000 core reach", use optimize_selection (Instagram only, 5 credits). It searches an analysis's already-scraped data for the best subset, so it doesn't scrape again.

1. create_creator_list for the brief, so the run always ends with a list.
2. analyze_creators with 15–30 candidates, then wait_for_job.
3. optimize_selection(analysis_id, min_core_pct, min_core_reach, max_credits). It returns:
   • current and best sets, and whether the targets are met;
   • the gaps to the targets;
   • drag_creators: removing them raises core %;
   • suggested_additions: already-scraped creators whose audience overlaps this core.
4. set_creator_list with best and a description holding its core % and core reach.
5. If the targets aren't met, drop the drag creators, add the suggestions (or discover_creators on a narrower subtopic when reach is short) and go back to step 2.

Stop when the targets are met, the budget is spent, or two rounds bring no improvement. The hit_audience_targets prompt runs this loop for you.