docs: architecture, guidelines, domain designs, progressive code index

docs/code_index/catalog.md

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+# Index: Catalog
+
+Domain design: `docs/domains/catalog.md`. Specs: `openspec/specs/product/`,
+`category/`, `brand/`.
+
+## Backend (`apps/api`)
+
+| File | Holds |
+|---|---|
+| `src/modules/product/service.rs` | public list/detail, merchant CRUD, publish/unpublish, SKU upsert, template link validation |
+| `src/modules/product/repo.rs` | SKU attach + sold_count aggregation |
+| `src/modules/category/` | public category tree |
+| `src/modules/brand/` | public list; admin whole-list replacement |
+| `migrations/0003_catalog.sql`, `0005_seed_category_tree.sql`, `0008_brands.sql` | schema + seeds |
+
+## Shared contract
+
+`types.ts`: `Product`, `Sku`, `Category`, `Brand`, `ProductStatus`.
+`api.ts`: `listProducts`, `getProduct`, `listCategories`, `listBrands`,
+`shop.*` product/SKU methods, `admin.replaceBrands`.
+
+## Frontends
+
+- Mall: `pages/index.vue` (floors), `pages/search.vue`, `pages/goods/[id].vue`,
+  `components/ui/ProductCard.vue`
+- Shop-admin: `pages/products/{index,new,[id]}.vue`,
+  `components/ProductForm.vue`
+- Admin: `pages/brands.vue`