fix: 修复商品图片管理和缓存一致性问题

- 重构 ImageUpload 组件，使用 rawUrl 跟踪原始路径
- 新增 normalizeStorageImageUrl 避免存储绝对 URL
- 商品增删改后同步清除缓存和旧图片文件
- 修复秒杀活动列表商品图片为空的问题

flash-sale-frontend/src/utils/normalizers.ts

@@ -16,7 +16,7 @@ import type {
   AdminRecentOrderRow,
   AdminUserRow,
 } from '@/types/admin'
-import { DEFAULT_PRODUCT_IMAGE, resolveImageUrl } from '@/utils/image'
+import { DEFAULT_PRODUCT_IMAGE, normalizeStorageImageUrl, resolveImageUrl } from '@/utils/image'
 
 const toNumber = (value: unknown, fallback = 0) => {
   const result = Number(value)
@@ -280,7 +280,7 @@ export const normalizeAdminProduct = (product: Record<string, any>): AdminProduc
   price: toNumber(product.price),
   stock: toNumber(product.stock),
   status: toNumber(product.status, 1),
-  imageUrl: resolveImageUrl(toString(product.imageUrl, '')),
+  imageUrl: normalizeStorageImageUrl(toString(product.imageUrl, '')),
   createdAt: toIsoLikeString(product.createdAt),
   updatedAt: product.updatedAt ? toIsoLikeString(product.updatedAt) : undefined,
   totalSales: toNumber(product.totalSales),