findById(id: TicketId): Option[Ticket]を追加
createIssue(title: String): Issueを追加
createBug(title: String, description: String): Bugを追加
findIssuesByStatus(staus: String): Option[Seq[Issue]]を追加
findBugsByStatus(status: String): Option[Seq[Bug]]を追加
fix(id: TicketId): Booleanを追加