Extend retrieval features and refresh documentation

[cpdata]

Summary

• add vector-only, regex, exact-match, and rerank retrieval helpers with MeshMind client wrappers
• refresh the example script, README_LATEST, and supporting docs to reflect CRUD, triplet, and retrieval updates
• expand developer tooling with pytest fixtures, Makefile targets, and a CI workflow that runs formatting checks and tests

Testing

• pytest (fails: ModuleNotFoundError: No module named 'numpy')

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https://chatgpt.com/codex/tasks/task_b_68ee1c9ee92c83218cbbebce8b0667b8