Add native Git-backed pipeline loading

[eugene-panin]

Summary

• load pipeline DAGs through Airflow GitDagBundle
• add one-command Git repository launcher with public and SSH support
• keep local bind mounts as a separate development fallback
• verify native Git loading in CI

Local verification

• image build and pip check passed
• local-path runtime and storage smoke DAGs passed
• public Git bundle loaded commit e812e52 and both smoke DAGs passed
• private SSH repository built and loaded its DAG at commit 44d8bcc

No real pipeline database or object data was modified.