feat: 书库导入导出/图片变体/书籍搜索/小组件运行时等

新增：
- 书库导入导出（library_import/library_export）及测试
- 图片变体生成（image_variants）与响应式图片（responsiveImage）
- 书籍搜索（bookSearch）+ BookSearch/LibrarySearchGrid 组件
- 小组件运行时（widgetRuntime）与静态检查（widgetLint）
- 上传缓存中间件（upload_cache）与字体 CSS 提取脚本

其它：
- 后端 handlers/services 全量调整
- 前端页面、组件、库函数与配置更新

backend/handler/handlers.go

@@ -10,36 +10,36 @@ import (
 
 // Handlers 聚合所有服务引用
 type Handlers struct {
-	Ops          *service.Operations
-	Cfg          *config.Config
-	Hub          *realtime.Hub
-	Auth         *service.AuthService
-	Board        *service.BoardService
-	Post         *service.PostService
-	Comment      *service.CommentService
-	Like         *service.LikeService
-	Favorite     *service.FavoriteService
-	Follow       *service.FollowService
-	Notification *service.NotificationService
-	OverviewSvc  *service.OverviewService
-	Checkin      *service.CheckinService
-	Announcement *service.AnnouncementService
-	SitePage     *service.SitePageService
-	Upload       *service.UploadService
-	PostFile     *service.PostFileService
-	Points       *service.PointsService
-	Setting      *service.SettingService
-	AdminUser    *service.AdminUserService
-	LegacyImport *service.LegacyImportService
-	Moderation   *service.ModerationService
-	Chat         *service.ChatService
-	Visit        *service.VisitStatsService
-	Analytics    *service.AnalyticsService
-	HidePwd      *service.HidePasswordCookie
-	Ads          *service.AdService
-	Sidebar      *service.SidebarService
-	FriendLink   *service.FriendLinkService
-	Badge        *service.BadgeService
+	Ops            *service.Operations
+	Cfg            *config.Config
+	Hub            *realtime.Hub
+	Auth           *service.AuthService
+	Board          *service.BoardService
+	Post           *service.PostService
+	Comment        *service.CommentService
+	Like           *service.LikeService
+	Favorite       *service.FavoriteService
+	Follow         *service.FollowService
+	Notification   *service.NotificationService
+	OverviewSvc    *service.OverviewService
+	Checkin        *service.CheckinService
+	Announcement   *service.AnnouncementService
+	SitePage       *service.SitePageService
+	Upload         *service.UploadService
+	PostFile       *service.PostFileService
+	Points         *service.PointsService
+	Setting        *service.SettingService
+	AdminUser      *service.AdminUserService
+	LegacyImport   *service.LegacyImportService
+	Moderation     *service.ModerationService
+	Chat           *service.ChatService
+	Visit          *service.VisitStatsService
+	Analytics      *service.AnalyticsService
+	HidePwd        *service.HidePasswordCookie
+	Ads            *service.AdService
+	Sidebar        *service.SidebarService
+	FriendLink     *service.FriendLinkService
+	Badge          *service.BadgeService
 	LeaderboardSvc *service.LeaderboardService
 	LibrarySvc     *service.LibraryService
 }