Add schedule-level timeout/retry controls for backup and cloud backup

[Copilot]

Scheduled backups could hang indefinitely, and cloud sync had no per-schedule retry policy. This PR adds schedule-configurable timeout/retry controls for both backup and cloud backup, and applies them at task execution time so timed-out attempts are retried before final failure.

• Schema + persistence

  • Added backup_timeout_seconds, backup_retry_count, cloud_sync_timeout_seconds, cloud_sync_retry_count to schedules.
  • Added Alembic migration to persist new fields with retry defaults (0).

• API/model wiring

  • Extended schedule create/update/read schemas and schedule creation validation to accept/normalize the new fields.
  • Passed these fields through schedule API/service layers into scheduled BackupRequest.

• Task definition propagation

  • Extended TaskDefinitionBuilder to attach backup/cloud-sync timeout + retry values to task definitions.
  • Plumbed those values through JobService and scheduler-triggered job creation.

• Execution behavior (backup + cloud sync)

  • Implemented timeout + retry loops in BackupTaskExecutor and CloudSyncTaskExecutor.
  • Each task now:
    • enforces per-task timeout (when configured),
    • retries up to configured count,
    • reports timeout/retry attempts in task output,
    • fails only after all attempts are exhausted.

• UI updates (Schedules)

  • Added create/edit form inputs for backup/cloud timeout and retry counts.
  • Added schedule list summary line showing configured retry/timeout policy.

# Scheduled run now carries per-schedule execution policy
backup_request = BackupRequest(
    repository_id=repository.id,
    source_path=schedule.source_path,
    cloud_sync_config_id=schedule.cloud_sync_config_id,
    backup_timeout_seconds=schedule.backup_timeout_seconds,
    backup_retry_count=schedule.backup_retry_count,
    cloud_sync_timeout_seconds=schedule.cloud_sync_timeout_seconds,
    cloud_sync_retry_count=schedule.cloud_sync_retry_count,
)