Create an end-to-end Jupyter notebook example

[varunreddy]

Summary

Add a Jupyter notebook that walks through the full SkillMesh workflow: loading a registry, retrieving cards, emitting context, and using the result in a mock agent loop.

Acceptance Criteria

• Create examples/notebooks/getting-started.ipynb
• Demonstrate: install, load registry, retrieve top-K, emit context for claude/codex
• Include markdown cells explaining each step
• Show sample output inline
• Notebook runs cleanly from top to bottom