feat(public): 商品详情页展示厂商建议零售价(MSRP)

后端 ProductByID/ProductByGTIN 在商品详情 JSON 中内嵌 msrp 字段（按 effective_date 倒序，过滤 amount=0 的无效快照）；公开前台详情页新增「建议零售价」展示。

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

public-frontend/src/components/ProductView.tsx

@@ -42,6 +42,12 @@ export default function ProductView({ id, onBack }: { id: string; onBack: () =>
   const nutriEntries = Object.entries(p.nutriments || {}).filter(
     ([, v]) => v !== null && v !== undefined,
   );
+  const latestMsrp = (p.msrp || [])[0];
+  const msrpText = latestMsrp
+    ? latestMsrp.currency === "CNY"
+      ? `¥${latestMsrp.amount.toFixed(2)}`
+      : `${latestMsrp.amount.toFixed(2)} ${latestMsrp.currency}`
+    : null;
 
   return (
     <div>
@@ -93,6 +99,17 @@ export default function ProductView({ id, onBack }: { id: string; onBack: () =>
             }
           />
           <Row label="产地" value={p.country_of_origin} />
+          <Row
+            label="建议零售价"
+            value={
+              msrpText ? (
+                <span className="inline-flex items-baseline gap-2">
+                  <span className="font-medium text-gray-900">{msrpText}</span>
+                  <span className="text-xs text-gray-400">厂商建议，仅供参考</span>
+                </span>
+              ) : null
+            }
+          />
           <Row label="Nutri-Score" value={p.nutri_score} />
           <Row label="配料" value={p.ingredients_text} />
           <Row