Editor: discard changes, reliable variant saves & smarter defaults

Several product-editor improvements that make everyday editing safer and less surprising.

New

• Discard changes — Product and category editors now have a Cancel Changes button that appears when you have unsaved edits and reverts everything to the last saved version (after a confirmation). The brand editor already had this.

Fixed

• Variants save with the product — Clicking Update Product now saves your variant edits too (for example, a removed variant), instead of requiring a separate "Save Options & Variants" click.
• Clearer validation — When a required field needs attention, the editor now jumps to and highlights the correct section, instead of showing a warning that pointed at the top navigation.

Improved

• Newest products first — The product list now shows the most recently added products at the top by default.