Seasonal Pre-Build Planner

Pick an item + work center to see level production vs. seasonal forecast, on-hand riding between the safety-stock floor and seasonal-max ceiling, and a feasibility verdict against the work center's effective hours. Not built this session: the SEASONAL-mode items in this data (107 of them) have no Routing loaded — the only ~85 parts with routings (the flexi line) classify as MTO_BATCH, not SEASONAL. A real chase-vs-level-load demo needs an item that is both, and none exists yet in the loaded scope. Ready to wire up as soon as routing coverage extends to a seasonal item — the underlying math (engine/capacity.ts, computeAnticipationStock/computeSeasonalMax) is already built and tested.