- Add size_id, units_produced, quantity_g to batches table
- quantity_g auto-calculated from units × packing size on save
- Batch model deducts spice quantities on create, reverses on delete,
recalculates on update when relevant fields change
- Batch form shows live total weight preview
- Chargen table shows units + grams produced
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>