Replace fabricated eval stubs with actual gold files and seed-data from
adk-core: payment_overdue (formula field), AssetFedexValidationRule
(validation rule with lookup deps), QueueableWithCalloutRecipes (Apex
with class dependencies).
New skill that generates minimal seed-data stubs (custom fields, objects,
Apex class stubs) for evaluation datasets in the afv-library. Adapted from
the adk-eval-seed-data-generator with afv-library conventions and all
PR #194 review feedback addressed (scoped allowed-tools, no hardcoded
paths, progressive disclosure, skills referenced by name).
