feat(api): add customer accounts with live summary and append-only ledger

One balance row per (user, kind, currency): available and frozen carry the
platform base currency, points carries none. Monetary and points rows use
separate partial unique indexes because a plain UNIQUE lets NULL repeat.

Balance changes go through transactional primitives that debits guard with a
conditional update, credits add atomically, and freeze/release move both sides
in one transaction after locking rows by primary key. Every change appends an
immutable entry holding its resulting balance. Registration and a migration
backfill create the zero rows; GET /api/me/stats is the only public surface and
no endpoint mutates a balance.

The mall buyer center and points page drop the USER_STATS fixture for the
shared contract; the fixture stays exported so the fixed-data adapter can still
serve the account domain as a rollback path.

Implements openspec change add-customer-accounts.

apps/mall/pages/integral.vue

@@ -1,11 +1,28 @@
 <script setup lang="ts">
+import type { AccountSummary } from "@vmall/shared";
 import { t as pick } from "@vmall/shared";
-import { INTEGRAL_PRODUCTS, USER_STATS } from "~/mock/data";
+// The catalog stays on fixtures until the points-mall change lands; the points
+// balance itself is live.
+import { INTEGRAL_PRODUCTS } from "~/mock/data";
 
 const { locale, t } = useI18n();
+const { $api } = useNuxtApp();
 const session = useSessionStore();
+const stats = ref<AccountSummary | null>(null);
 const redeemed = ref<Set<string>>(new Set());
 
+async function loadStats(): Promise<void> {
+  if (!session.isLoggedIn) {
+    stats.value = null;
+    return;
+  }
+  try {
+    stats.value = await $api.getAccountSummary();
+  } catch {
+    stats.value = null;
+  }
+}
+
 const breadcrumb = computed(() => [
   { label: t("stores.breadcrumbHome"), to: "/" },
   { label: t("marketing.integralBreadcrumb") },
@@ -19,7 +36,10 @@ function isRedeemed(id: string): boolean {
   return redeemed.value.has(id);
 }
 
-onMounted(() => session.hydrate());
+onMounted(() => {
+  session.hydrate();
+  void loadStats();
+});
 </script>
 
 <template>
@@ -35,7 +55,7 @@ onMounted(() => session.hydrate());
             <div>
               <p class="account-name">{{ session.user?.display_name }}</p>
               <p class="points-label">{{ t("marketing.pointsBalance") }}</p>
-              <strong class="account-points">{{ USER_STATS.points }}</strong>
+              <strong class="account-points">{{ stats ? stats.points : t("common.loading") }}</strong>
             </div>
           </template>
           <template v-else>