feat: prepare repo for open sourcing on GitHub

- Switch from Cursor Agent CLI to local vLLM/OpenAI-compatible API
- Update README to document vLLM setup and usage
- Update all Elastic references for personal GitHub repo
- Remove Buildkite CI and Elastic-specific configs
- Update CODEOWNERS, SECURITY.md, CONTRIBUTING.md for mitkox
- Add openai dependency for OpenAI-compatible API client

Author: qintarfermidiracstatistics981