Add Codex skill for sPyTial Python authoring

[sidprasad]

Summary

• add a new Codex skill at skills/add-spytial-python for integrating sPyTial into Python programs
• include CLRS-pattern-driven references for standard data structures
• include selector syntax and debugging guidance aligned with simple-graph-query
• add a starter scaffold script for linked-list/tree/graph/matrix integrations

Validation

• python3 /Users/siddharthaprasad/.codex/skills/.system/skill-creator/scripts/quick_validate.py skills/add-spytial-python
• python3 skills/add-spytial-python/scripts/scaffold_spytial_starter.py --shape tree --out /tmp/spytial_tree_starter.py --force
• python3 -m py_compile skills/add-spytial-python/scripts/scaffold_spytial_starter.py

Notes

• excludes existing unrelated local change in demos/balancing.ipynb