Missing age_group attribute

Apparel feeds must declare age_group: newborn, infant, toddler, kids, or adult. Without it, products are disapproved.

Apparel feeds inherited from generic templates often lack the age_group field, especially when the catalog assumes adult by default.

1. Add age_group on every apparel product. Acceptable values: newborn, infant, toddler, kids, adult.
2. For mixed-audience products (unisex apparel), still pick the primary age_group.
3. Don't leave it blank — always assert one value.

• Using 'all', 'mixed', or custom values — Google only accepts the five enums