Nm Leyline Additive Bias Defense

- Initial release of the additive-bias-defense skill, ported from claude-night-market/leyline. - Establishes a defense against unnecessary code additions by inverting the burden of proof: all new additions must be explicitly justified. - Introduces a set of five scrutiny questions and six anti-pattern signals to evaluate proposed changes. - Defines a clear burden-of-proof verdict system: justified, needs_evidence, or unjustified. - Outlines integration expectations for review-oriented skills and references related supporting skills. - Promotes the subtraction principle: consider removals or simpler alternatives before accepting additions.