Run a single warming pass on Pinterest — scroll the home feed, save 1-3 pins, react (heart) on 1-2, optionally follow one creator. First arg is an optional brand slug (defaults to default_brand in config/brand.json). Reads cadence from config/engagement-schedule.json, brand tunables (own handle, topic regex, parody-risk handles) from config/brand.json. Use when the user says "warm pinterest", "engage on pinterest", or runs /pinterest-warm. Also called by /warm-all on a schedule.
