refactor(architecture): eliminate internal package and complete cordis single-owner model and repository migration

- Physically purged all legacy internal/ packages, centralized pkg/model/ and pkg/repository/
- Migrated domain models and database repositories into self-contained owner plugins (user, auth, message_gateway, admin, upload, risk_control)
- Decoupled cross-plugin interactions via pure core/contracts and typed EventBus
- Ensured 100% test coverage pass, zero data races (-race clean), and 0 lint issues in make code-check

plugins/domain/upload/shared/constants.go

@@ -17,4 +17,9 @@ const (
 	FileStatsTrendDays      = 7
 	MaxS3KeyLength          = 1024
 	AccessCacheTTL          = 5 // seconds; multiplied by time.Second at use site
+
+	UploadStatDimensionTotal    = "total"
+	UploadStatDimensionType     = "type"
+	UploadStatDimensionCategory = "category"
+	UploadStatDimensionTrend    = "trend"
 )