Agent Skills: active-record-validations

Expert guidance for Active Record validations in Rails 8.1. Use when adding validations, writing "validates", "validate", working with "errors", "valid?", "invalid?", building custom validators, handling uniqueness, presence, format validation, numericality, conditional validations, strict validations, or normalizations. Covers model-layer data integrity, DB constraint pairing, error handling, and common pitfalls.