refactor: eliminate string/magic-number literals (goconst, mnd) and fix const-type grouping (SA9004)

- upload/task: taskCategoryUpload/taskQueueDefault 常量替代 8 处字面量
- admin: 复用既有 logDBNameSQLite 常量替代 3 处 "sqlite" 字面量
- pkg/cache/disk: defaultCleanupInterval 命名常量
- driver_asynq_worker/executor: 分离 contextKey 类型常量组
lint_issues 45→34, tests 44/44

backend/plugins/domain/upload/task/cleanup.go

@@ -36,7 +36,7 @@ var SystemCleanupMeta = contracts.TaskMetaDTO{
 	Description: "定期清理未使用上传文件、历史推送记录和过期任务执行日志",
 	Category:    "maintenance",
 	MaxRetry:    3,
-	Queue:       "default",
+	Queue:       taskQueueDefault,
 }
 
 // SystemCleanupHandler 系统定期垃圾清理异步任务处理器

backend/plugins/domain/upload/task/rebuild_stats.go

@@ -27,9 +27,9 @@ var RebuildUploadStatsMeta = contracts.TaskMetaDTO{
 	Name:        RebuildUploadStatsTask,
 	DisplayName: "重算文件存储统计",
 	Description: "根据当前 w_uploads 活跃记录全量重建 w_upload_stats（总量、类型、分类、趋势）",
-	Category:    "upload",
+	Category:    taskCategoryUpload,
 	MaxRetry:    3,
-	Queue:       "default",
+	Queue:       taskQueueDefault,
 }
 
 // RebuildUploadStatsHandler rebuilds incremental upload stats from active upload records.

backend/plugins/domain/upload/task/storage_migration.go

@@ -39,9 +39,9 @@ var StorageMigrationMeta = contracts.TaskMetaDTO{
 	Name:        StorageMigrationTask,
 	DisplayName: "迁移文件存储",
 	Description: "将活动存储中的文件迁移到待切换的目标存储，迁移期间文件系统保持只读",
-	Category:    "upload",
+	Category:    taskCategoryUpload,
 	MaxRetry:    3,
-	Queue:       "default",
+	Queue:       taskQueueDefault,
 	Params: []contracts.TaskParamDTO{
 		{
 			Name:        "target",

backend/plugins/domain/upload/task/tasks.go

@@ -17,6 +17,12 @@ import (
 	"sync"
 )
 
+// 上传域任务的通用元数据常量（TaskMetaDTO Category/Queue 复用）
+const (
+	taskCategoryUpload    = "upload"
+	taskQueueDefault      = "default"
+)
+
 const (
 	// WarmImageCacheTask 图片压缩缓存预热任务标识
 	WarmImageCacheTask = "upload:warm_image_cache"
@@ -31,9 +37,9 @@ var WarmImageCacheMeta = contracts.TaskMetaDTO{
 	Name:        WarmImageCacheTask,
 	DisplayName: "预热图片压缩缓存",
 	Description: "串行将文件管理中的图片转换为指定质量的 WebP 并写入永久缓存",
-	Category:    "upload",
+	Category:    taskCategoryUpload,
 	MaxRetry:    3,
-	Queue:       "default",
+	Queue:       taskQueueDefault,
 	Params: []contracts.TaskParamDTO{
 		{
 			Name:        "quality",