Agent Skills: wc-archetype-mutation

The mutation operator for the FIFA World Cup Fantasy evolution engine. Applies small, bounded, feasibility-preserving perturbations to a recombined offspring squad/plan — swap one differential for an adjacent-price alternative, reorder the bench by kickoff, shift one captain-ladder step, try one fixture-swing transfer, nudge one enabler. Mutation rate is low by default and raised on demand by the diversity governor when the population has collapsed. Each mutation stays inside budget/nation/formation feasibility. Use in the mutate stage after recombination, or when wc-population-diversity calls for more exploration.