cold-experiment

Design the next A/B experiment for the autoresearch loop. Reads the current tier from .cold/config.json, picks the variable to test, drafts arm specs (e.g. statement vs. question subject lines), declares sample size + success criteria, and writes a protocol to .cold/experiments/. Use after /cold offer and before /cold draft. The experiment protocol is what cold-draft reads to generate variant pairs. Use when the…