fix: dataset integrity - pruned 67 malformed items

fix: shuffle MCQ candidates, fix length bias, add difficulty tracking

fix: removed all duplicate candidates across the benchmark using rigorous multi-pass review

feat: Artisan Wave 8 completion. 3030 hand-crafted items without templates

feat: release v1.0 (1,200 handcrafted items, 16 modules, 0% contamination)