0.0.5

feat: graceful exam.yml handling — candidate can always enter workspace

  - Backend: add ExamConfigService to read/cache exam.yml from container
  - Backend: startInterview catches ExamConfigNotFoundException and skips checkpoint init instead of failing — interview starts regardless
  - Frontend: remove deleted CheckpointResponse type, add local CheckpointInfo
  - Frontend: checkpoint panel shows virtual end node + "考試內容由面試官確認" when checkpoints are empty (exam.yml absent), with unconditional 結束測試 button