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>

api/internal/handler/openapi.json

@@ -208,7 +208,22 @@
           "nutriments": { "type": "object", "additionalProperties": true, "nullable": true },
           "nutrition_basis": { "type": "string", "nullable": true },
           "nutri_score": { "type": "string", "nullable": true },
-          "ingredients_text": { "type": "string", "nullable": true }
+          "ingredients_text": { "type": "string", "nullable": true },
+          "msrp": {
+            "type": "array",
+            "description": "Manufacturer suggested retail price snapshots (reference only, newest first; zero-amount entries omitted).",
+            "items": {
+              "type": "object",
+              "properties": {
+                "amount": { "type": "number" },
+                "currency": { "type": "string" },
+                "region": { "type": "string" },
+                "effective_date": { "type": "string", "nullable": true },
+                "source_url": { "type": "string", "nullable": true },
+                "note": { "type": "string", "nullable": true }
+              }
+            }
+          }
         }
       }
     }

api/internal/store/store.go

@@ -126,6 +126,7 @@ type Product struct {
 	Ingredients     *string        `json:"ingredients_text,omitempty"`
 	Allergens       []string       `json:"allergens,omitempty"`
 	Additives       []string       `json:"additives,omitempty"`
+	MSRP            []MSRP         `json:"msrp,omitempty"`
 }
 
 // ProductBarcodes returns every barcode attached to a product, primary first.
@@ -280,6 +281,9 @@ func (s *Store) ProductByGTIN(ctx context.Context, gtin string) (*Product, error
 	if p.Specs, err = s.buildSpecs(ctx, p.ArchiveKind, attrs); err != nil {
 		return nil, err
 	}
+	if p.MSRP, err = s.ListMSRP(ctx, p.ID); err != nil {
+		return nil, err
+	}
 	s.cacheSet(ctx, suffix+gtin, p, productCacheTTL)
 	return p, nil
 }
@@ -301,6 +305,9 @@ func (s *Store) ProductByID(ctx context.Context, id string) (*Product, error) {
 	if p.Specs, err = s.buildSpecs(ctx, p.ArchiveKind, attrs); err != nil {
 		return nil, err
 	}
+	if p.MSRP, err = s.ListMSRP(ctx, p.ID); err != nil {
+		return nil, err
+	}
 	s.cacheSet(ctx, suffix+id, p, productCacheTTL)
 	return p, nil
 }
@@ -445,11 +452,12 @@ type MSRP struct {
 	Note          *string `json:"note"`
 }
 
-// ListMSRP returns all MSRP snapshots for a product.
+// ListMSRP returns a product's suggested-retail-price snapshots, newest first.
+// Zero-amount entries are excluded as they carry no price information.
 func (s *Store) ListMSRP(ctx context.Context, id string) ([]MSRP, error) {
 	rows, err := s.pool.Query(ctx,
 		`SELECT amount, currency, region, effective_date::text, source_url, note
-		 FROM product_msrp WHERE product_id = $1 ORDER BY effective_date DESC NULLS LAST`, id)
+		 FROM product_msrp WHERE product_id = $1 AND amount > 0 ORDER BY effective_date DESC NULLS LAST`, id)
 	if err != nil {
 		return nil, err
 	}