feat(mall): restore real brand and sales facets

Wave 6, the last substantive piece of the mock-API migration. Wave 1 removed the
brand facet and the sales/comments sorts for want of a model; sales turn out to
be derivable from order_items and a brand model is a table plus a column.

- a `brands` table with a nullable `products.brand_id` and an ordered admin
  replace, mirroring categories and storefront content; a public `GET /api/brands`
  and a `brand_id` filter on the catalog, which the search page's facet uses
- `sold_count` per product, computed from `order_items` joined to orders that
  reached payment, so an abandoned or cancelled checkout cannot count as a sale.
  It is computed per read rather than stored, so it cannot drift from the orders
  that produced it
- `sort=sales` alongside `sort=price`; anything else is still a 400
- merchants can set a product's brand through the existing product upsert
- the review UI is gone: the card's review figure and the product detail page's
  reviews tab, summary and replies. There is no reviews model, and the mall
  attributed invented comments to named shoppers and showed a "good rate". The
  now-unreferenced fabrication helpers went with it (`salesOf`, `commentCountOf`,
  `commentsFor`, `commentStats`, `salesRankFor`, `productDetail`, `storeDetail`)

Two bugs found by checking rather than trusting: the fixed-data `listProducts`
had silently ignored `brand_id`, `sort` and `order`, so the restored facet
rendered but filtered nothing until the rollback check caught it; and the seed's
brand lookup read back through the shared `r` variable the product loop
reassigns, working once and then throwing.

Verified: 29 backend tests green including a new brand-and-sales case; all three
frontends build; searching filters by brand (24 to 6) and sorts by sales with
counts matching the API; a product page offers detail and after-sale tabs only,
with a real sold count; the fixed-data rollback filters by brand too.

OpenSpec change: openspec/changes/replace-mock-api-wave-6

apps/mall/pages/search.vue

@@ -1,10 +1,10 @@
 <script setup lang="ts">
 import { t as pick } from "@vmall/shared";
-import type { Category, Paged, Product } from "@vmall/shared";
+import type { Brand, Category, Paged, Product } from "@vmall/shared";
 
-// Only sorts the catalog model can answer. Brand and sales/comment facets were
-// removed in Wave 1: no backend model backs them.
-type SortType = "default" | "price";
+// Sorts the catalog model can answer: price and real sales. Comments still have
+// no model, so that facet stays out.
+type SortType = "default" | "price" | "sales";
 type OrderType = "asc" | "desc";
 
 const route = useRoute();
@@ -17,13 +17,17 @@ const queryValue = (value: unknown): string => {
   return typeof value === "string" ? value : "";
 };
 
+const parseSort = (raw: string): SortType =>
+  raw === "price" || raw === "sales" ? raw : "default";
+
 const state = computed(() => {
-  const sort: SortType = queryValue(route.query.sort) === "price" ? "price" : "default";
+  const sort = parseSort(queryValue(route.query.sort));
   const order: OrderType = queryValue(route.query.order) === "asc" ? "asc" : "desc";
   const pageValue = Number.parseInt(queryValue(route.query.page), 10);
   return {
     q: queryValue(route.query.q),
     category: queryValue(route.query.category),
+    brand: queryValue(route.query.brand),
     sort,
     order,
     page: Number.isFinite(pageValue) && pageValue > 0 ? pageValue : 1,
@@ -38,8 +42,9 @@ const { data: result } = await useAsyncData(
     $api.listProducts({
       q: state.value.q || undefined,
       category_id: state.value.category || undefined,
-      sort: state.value.sort === "price" ? "price" : undefined,
-      order: state.value.sort === "price" ? state.value.order : undefined,
+      brand_id: state.value.brand || undefined,
+      sort: state.value.sort === "default" ? undefined : state.value.sort,
+      order: state.value.sort === "default" ? undefined : state.value.order,
       page: state.value.page,
       per_page: 20,
     }),
@@ -55,11 +60,17 @@ const topLevelCategories = computed(() =>
   allCategories.value.filter((category) => category.parent_id === null).sort(byPosition),
 );
 
+// Shared with the product page; the fixed-data adapter serves the same list.
+const { data: brands } = await useAsyncData("brands", () => $api.listBrands(), {
+  default: () => [] as Brand[],
+});
+
 const replaceQuery = async (patch: Record<string, string | undefined>): Promise<void> => {
   const next: Record<string, string> = {};
   for (const [key, value] of Object.entries({
     q: state.value.q,
     category: state.value.category,
+    brand: state.value.brand,
     sort: state.value.sort,
     order: state.value.order,
     page: String(state.value.page),
@@ -79,6 +90,10 @@ const chooseCategory = (id?: string): void => {
   void replaceQuery({ category: id, page: "1" });
 };
 
+const chooseBrand = (id?: string): void => {
+  void replaceQuery({ brand: id, page: "1" });
+};
+
 const chooseSort = (sort: SortType): void => {
   const order: OrderType = state.value.sort === sort && sort !== "default"
     ? state.value.order === "asc" ? "desc" : "asc"
@@ -118,6 +133,7 @@ const breadcrumbItems = computed(() => [
 const sortOptions = computed(() => [
   { key: "default" as SortType, label: t("search.defaultSort") },
   { key: "price" as SortType, label: t("search.price") },
+  { key: "sales" as SortType, label: t("search.sales") },
 ]);
 </script>
 
@@ -155,6 +171,19 @@ const sortOptions = computed(() => [
             >{{ pick(category.name, locale) }}</button>
           </div>
         </div>
+        <div v-if="brands.length" class="filter-row">
+          <strong>{{ t("search.brand") }}</strong>
+          <div class="filter-options">
+            <button type="button" :class="{ active: !state.brand }" @click="chooseBrand()">{{ t("search.all") }}</button>
+            <button
+              v-for="brand in brands"
+              :key="brand.id"
+              type="button"
+              :class="{ active: brand.id === state.brand }"
+              @click="chooseBrand(brand.id)"
+            >{{ pick(brand.name, locale) }}</button>
+          </div>
+        </div>
         <div class="filter-row sort-row">
           <strong>{{ t("search.sort") }}</strong>
           <div class="filter-options">