Add SO-101 runtime image smoke validation

[sanjeevm0]

Summary

Add dedicated CI smoke coverage for gpu-offload/examples/so101-real-hardware/docker/Dockerfile. The current GPU-offload smoke workflow validates the core controller/runtime images but does not build or start the SO-101 runtime image.

This follow-up was identified during review of #1646.

Acceptance criteria

• Build gpu-offload/examples/so101-real-hardware/docker/Dockerfile in CI without requiring robot hardware.
• Start the resulting image in a hardware-independent smoke mode.
• Verify the expected LeRobot, remoter runtime, and SO-101 application imports succeed.
• Verify the configured container entrypoint starts and reaches a deterministic smoke-check result without connecting to robot hardware.
• Run the smoke check when the Dockerfile, its runtime dependencies, or relevant GPU-offload workflow files change.
• Fail the PR validation job when image construction, imports, or entrypoint startup regress.