- Split woo_price into woo_regular_price and woo_sale_price
- Sync to WC: if standard=0 sets regular_price, otherwise sets sale_price
- Validation: standard price cannot be less than sale price
- Both prices shown in mapping UI with sale price highlighted in green
- Refresh Prices pulls both values from WC API
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>