Add onboarding notebooks for the Python SDK

[AnuradhaKaruppiah]

Summary

Add a newcomer-facing Jupyter notebook tour of the NeMo Fabric Python SDK.

Scope

• Add a quickstart notebook covering typed configuration, planning, doctor checks, one-shot runs, normalized results, and stateful runtimes.
• Add a variations notebook covering available harnesses, skills, MCP servers, and optional NeMo Relay tracing.
• Add the missing Claude configuration variant and corresponding example contract coverage.
• Provide a lightweight notebook launch command and link the notebooks from the examples documentation.

Acceptance criteria

• Notebooks are committed without outputs and execute end to end when prerequisites are available.
• Missing harness prerequisites degrade to useful configuration inspection and guidance.
• Generated artifacts and Jupyter checkpoints remain ignored.
• Example tests cover the added Claude variant.

Implementation

• feat: add onboarding notebooks for the Python SDK #58

[linear]

FABRIC-89