BizCore v6.2 - Mundo Checkout + Product Gallery

SAFE ADDITIVE UPDATE
- Product thumbnail/main image + up to 4 gallery images.
- Existing Mundo single image remains the thumbnail.
- Gallery images appear on product detail page.
- Checkout validation and duplicate-submit protection.
- Existing stock/order/seller/finance data is not reset.

INSTALL
1. Upload this ZIP to the ceylongemx.online BizCore root.
2. Extract with overwrite/replace enabled.
3. Open /update-6.2.php as Super Admin.
4. Add thumbnail/gallery images from Mundo Online Products.
5. Open Mundo and test Product -> Cart -> Checkout -> BizCore Online Orders.
