Agent Skills: resonance-ops-second-opinion

Independent second-model review for concrete diffs and decision artifacts. Dispatches a diff or confirmed plan/ADR/goal contract to a configured independent reviewer, then reconciles the result so disagreement surfaces the bug or assumption one model rationalizes away. Use before merging a risky change, as the final gate in a goal loop, before a high-risk one-way decision, or when the user asks for a second opinion, cross-model review, independent check, or decision review.