fix: default cover url

mengyastore-backend/internal/storage/jsonstore.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"strings"
 	"sync"
 	"time"
 
@@ -13,6 +14,8 @@ import (
 	"mengyastore-backend/internal/models"
 )
 
+const defaultCoverURL = "https://img.shumengya.top/i/2026/01/04/695a55058c37f.png"
+
 type JSONStore struct {
 	path string
 	mu   sync.Mutex
@@ -185,6 +188,10 @@ func (s *JSONStore) writeAll(items []models.Product) error {
 }
 
 func normalizeProduct(item models.Product) models.Product {
+	item.CoverURL = strings.TrimSpace(item.CoverURL)
+	if item.CoverURL == "" {
+		item.CoverURL = defaultCoverURL
+	}
 	if item.ScreenshotURLs == nil {
 		item.ScreenshotURLs = []string{}
 	}