feat(wish-tree): 许愿树页面微调七项

1. 背景图 aspectFill 撑满全屏，挂载点坐标按裁剪比例重算，便签不再落在图外
2. 写下心愿按钮单行不换行，缩小尺寸
3. 移除页面内许愿树标题/数量/最近心愿，点击便签弹出便签式详情卡
4. 默认请求100条：最新50条挂树，其余以弹幕形式缓缓飘过
5. MAKE A WISH 下方增加顶级位置轮播（购买后24小时内展示），点击弹出金色便签详情，与普通便签区分
6. 多棵树分屏轮播（swiper），背景图从服务器获取，带指示点
7. 后端：WishTree新增image字段，Wish新增isTop运行时标记，图片用go:embed内嵌随二进制部署，/images路由提供访问

server/internal/config/database.go

@@ -56,6 +56,13 @@ func autoMigrate() error {
 
 // seedDefaultData 初始化默认数据
 func seedDefaultData() error {
+	// 补充已有许愿树的背景图（新增字段后老数据为空）
+	if err := DB.Model(&model.WishTree{}).
+		Where("image = '' OR image IS NULL").
+		Update("image", "/images/trees/tree-1.jpg").Error; err != nil {
+		return err
+	}
+
 	// 检查是否已有许愿树数据
 	var count int64
 	DB.Model(&model.WishTree{}).Count(&count)
@@ -65,9 +72,9 @@ func seedDefaultData() error {
 
 	// 插入默认许愿树
 	trees := []model.WishTree{
-		{Name: "祈福树", Description: "许下美好愿望，祈福平安顺遂", Type: "pine", MaxWishes: 100, Sort: 0, Status: 1},
-		{Name: "姻缘树", Description: "祈求姻缘美满，爱情甜蜜", Type: "sakura", MaxWishes: 50, Sort: 1, Status: 1},
-		{Name: "事业树", Description: "祈愿事业顺利，步步高升", Type: "bamboo", MaxWishes: 80, Sort: 2, Status: 1},
+		{Name: "祈福树", Description: "许下美好愿望，祈福平安顺遂", Type: "pine", Image: "/images/trees/tree-1.jpg", MaxWishes: 100, Sort: 0, Status: 1},
+		{Name: "姻缘树", Description: "祈求姻缘美满，爱情甜蜜", Type: "sakura", Image: "/images/trees/tree-1.jpg", MaxWishes: 50, Sort: 1, Status: 1},
+		{Name: "事业树", Description: "祈愿事业顺利，步步高升", Type: "bamboo", Image: "/images/trees/tree-1.jpg", MaxWishes: 80, Sort: 2, Status: 1},
 	}
 	if err := DB.Create(&trees).Error; err != nil {
 		return err