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/service/leaderboard_test.go

@@ -38,9 +38,9 @@ func TestEarnedPointsWindowAndExclusions(t *testing.T) {
 		{UserID: a, Delta: 5, Reason: model.PointReasonCheckin, Balance: 5, CreatedAt: now},
 		{UserID: a, Delta: 3, Reason: model.PointReasonReplyReward, Balance: 8, CreatedAt: now},
 		{UserID: a, Delta: 2, Reason: model.PointReasonStreakBonus, Balance: 10, CreatedAt: now.Add(-time.Hour)},
-		{UserID: a, Delta: -3, Reason: model.PointReasonUnlockPost, Balance: 7, CreatedAt: now},         // 支出不计
-		{UserID: users[1].ID, Delta: 8, Reason: model.PointReasonBountyRefund, Balance: 8, CreatedAt: now}, // 退回不计
-		{UserID: users[2].ID, Delta: 5, Reason: model.PointReasonCheckin, Balance: 5, CreatedAt: now},      // 封禁不计
+		{UserID: a, Delta: -3, Reason: model.PointReasonUnlockPost, Balance: 7, CreatedAt: now},                 // 支出不计
+		{UserID: users[1].ID, Delta: 8, Reason: model.PointReasonBountyRefund, Balance: 8, CreatedAt: now},      // 退回不计
+		{UserID: users[2].ID, Delta: 5, Reason: model.PointReasonCheckin, Balance: 5, CreatedAt: now},           // 封禁不计
 		{UserID: d, Delta: 5, Reason: model.PointReasonCheckin, Balance: 5, CreatedAt: weekAgo.Add(-time.Hour)}, // 窗口外
 	}
 	if err := db.Create(&ledgers).Error; err != nil {