feat(mall): serve home marketing content from the API

Wave 4 of replacing the fixed-data mock adapter, and the first capability the
mall never had a backend for: the home page's banners, promo tiles, quick links
and floor advert art move out of local arrays.

- four explicit tables (`banners`, `promos`, `quick_links`, `floor_adverts`)
  rather than one JSONB payload table, so Postgres enforces each shape
- a migration seeds them from the assets the page already rendered, so the flip
  is visually a no-op. Destinations are real routes now: the mock's promo links
  pointed at dangling `?category=c1` ids and its first banner used `sort=sales`,
  which the catalog API rejects
- `GET /api/content/home` is public and returns the four active, ordered lists,
  always including a key so a page can render a missing block
- `GET /api/admin/content` and `PUT /api/admin/content/{kind}` let a platform
  admin read everything and replace one kind transactionally, with positions
  reindexed from the submitted order and a rejected list changing nothing
- the mall's fixed-data adapter learns `getHomeContent`, and a `content` domain
  joins the per-domain switch so the rollback path still renders the page

Verified: 23 backend tests green including six new content tests; all three
frontends build; the home page renders the same four blocks as before, an admin
reorder and deactivation change the rendered carousel, and the fixed-data
rollback renders every block with the backend stopped.

OpenSpec change: openspec/changes/replace-mock-api-wave-4

apps/mall/pages/index.vue

@@ -1,26 +1,40 @@
 <script setup lang="ts">
-import type { Category, Product } from "@vmall/shared";
+import type { Category, HomeContent, Product } from "@vmall/shared";
 import { t as pick } from "@vmall/shared";
-import { MOCK_BANNERS, MOCK_PROMOS, MOCK_QUICK_LINKS } from "~/mock/data";
 
 interface HomeFloor {
   categoryId: string;
   name: Record<string, string>;
-  advImage: string;
+  advImage: string | null;
   advUrl: string;
   products: Product[];
 }
 
+const emptyContent: HomeContent = { banners: [], promos: [], quick_links: [], floor_adverts: [] };
+
 const { locale, t } = useI18n();
 const { $api } = useNuxtApp();
 
 // Shared with the shell's category menu, so this does not refetch the tree.
 const { data: categories } = await useAsyncData("shell-categories", () => $api.listCategories());
 
-// Floor structure comes from the category tree; floor products come from the
-// catalog API. Banner, promotion, quick-link and advert art stay local content.
+// Marketing content comes from the content API; an outage leaves these lists
+// empty rather than breaking the page.
+const { data: content } = await useAsyncData("home-content", () => $api.getHomeContent(), {
+  default: () => emptyContent,
+});
+
+const banners = computed(() =>
+  content.value.banners.map((banner) => ({ image: banner.image, url: banner.url })),
+);
+const quickLinks = computed(() => content.value.quick_links);
+const promos = computed(() => content.value.promos);
+
+// Floor structure comes from the category tree and floor products from the
+// catalog API; advert art is an ordered pool assigned to floors in turn.
 const { data: floors } = await useAsyncData("home-floors", async () => {
   const roots: Category[] = categories.value ?? (await $api.listCategories());
+  const adverts = content.value.floor_adverts;
   const tops = roots
     .filter((category) => category.parent_id === null)
     .sort((a, b) => a.position - b.position);
@@ -30,7 +44,7 @@ const { data: floors } = await useAsyncData("home-floors", async () => {
       const floor: HomeFloor = {
         categoryId: category.id,
         name: category.name,
-        advImage: `/mock/floor-adv-${(index % 6) + 1}.svg`,
+        advImage: adverts.length > 0 ? adverts[index % adverts.length].image : null,
         advUrl: `/search?category=${category.id}`,
         products: page.items,
       };
@@ -48,13 +62,13 @@ const visibleFloors = computed(() => floors.value ?? []);
     <div class="w1200 hero">
       <ShellCategoryMenu pinned />
       <div class="hero-slider">
-        <UiCarousel :images="MOCK_BANNERS" :height="450" />
+        <UiCarousel :images="banners" :height="450" />
       </div>
     </div>
 
     <div class="w1200 strip">
       <ul class="quick">
-        <li v-for="q in MOCK_QUICK_LINKS" :key="q.url + pick(q.label, 'en')">
+        <li v-for="q in quickLinks" :key="q.id">
           <NuxtLink :to="q.url">
             <svg viewBox="0 0 24 24" width="26" height="26" fill="currentColor"><path :d="q.glyph" /></svg>
             <span>{{ pick(q.label, locale) }}</span>
@@ -62,7 +76,7 @@ const visibleFloors = computed(() => floors.value ?? []);
         </li>
       </ul>
       <div class="promos">
-        <NuxtLink v-for="p in MOCK_PROMOS" :key="p.image" :to="p.url">
+        <NuxtLink v-for="p in promos" :key="p.id" :to="p.url">
           <img :src="p.image" :alt="t('home.hotPromo')" loading="lazy" />
         </NuxtLink>
       </div>
@@ -75,7 +89,7 @@ const visibleFloors = computed(() => floors.value ?? []);
           <NuxtLink :to="`/search?category=${floor.categoryId}`" class="more">{{ t("home.viewMore") }} ›</NuxtLink>
         </header>
         <div class="floor-body">
-          <NuxtLink :to="floor.advUrl" class="floor-adv">
+          <NuxtLink v-if="floor.advImage" :to="floor.advUrl" class="floor-adv">
             <img :src="floor.advImage" :alt="pick(floor.name, locale)" loading="lazy" />
           </NuxtLink>
           <div class="floor-grid">