Chengdong ZhangandClaude Sonnet 5
8446650baf
Rearranges the Rust backend by domain: `modules/catalog` bundled four distinct concepts (Product, SKU, Category, Brand) behind one router and one 392-line service file, unlike every other module in the codebase which owns exactly one bounded aggregate. Splits into `modules/product` (Product/SKU, publish lifecycle, shop-scoped CRUD), `modules/category` (category tree, subtree query), and `modules/brand` (brand list, admin replace-all). `Category`/`Brand` move out of the shared `models.rs` into their owning modules; `Product`/`Sku` stay since `favorite`/`flash_sale`/`group_buying` reference them across modules. Purely internal restructuring — no route, schema, or behavior changes. Implements openspec change split-catalog-into-product-category-brand. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>