feat(config): add expired box cleanup functionality

Adds dedicated config setting and cleanup logic for
managing expired content boxes via admin tools and CLI.

lib/config/models.go

@@ -49,6 +49,7 @@ const (
 	SettingSecurityUploadWindowSecs  = "security_upload_window_seconds"
 	SettingSecurityUploadMaxRequests = "security_upload_max_requests"
 	SettingSecurityUploadMaxGB       = "security_upload_max_gb"
+	SettingExpiredCleanupIntervalSecs = "expired_cleanup_interval_seconds"
 )
 
 type SettingType string
@@ -121,6 +122,7 @@ type Config struct {
 	SecurityUploadWindowSeconds int64
 	SecurityUploadMaxRequests   int
 	SecurityUploadMaxBytes      int64
+	ExpiredCleanupIntervalSeconds int64
 
 	sources  map[string]Source
 	values   map[string]string