fix(api): register ArtifactCleanupLauncher in scheduled jobs

[aaronsb]

Summary

Fixes the scheduled jobs manager failing to run artifact cleanup jobs due to missing launcher registration.

Changes

1. main.py: Added ArtifactCleanupLauncher to the launcher registry
2. artifact_cleanup.py: Added missing get_job_type() abstract method implementation

Error Fixed

❌ Unknown launcher: ArtifactCleanupLauncher

and

TypeError: Can't instantiate abstract class ArtifactCleanupLauncher with abstract method get_job_type

Test plan

• API starts without launcher errors
• Scheduled jobs manager starts successfully