Add CLI configuration and validation to core pipeline

[oyekamal]

Summary

• add an argparse-based CLI to core/core.py that reads transcript/audio paths and the API key from flags or environment variables with sensible defaults
• validate configuration before running, guard against missing transcripts, and keep downstream analytics from running on invalid responses
• update the README with the new configuration flow and usage examples for the CLI

Testing

• python -m compileall core/core.py

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https://chatgpt.com/codex/tasks/task_b_68ecc8f7f270832fa2b14ea56ec074d7