release: bump version to 0.2.4 and update CHANGELOG

Updated the version to 0.2.4 in `server.json`, `__init__.py`, `CITATION.cff`, and `CHANGELOG.md`. This release introduces significant enhancements, including the addition of `BCE_MCP_TOOLS` for tool advertisement control, `BCE_EMBEDDING_QUERY_TIMEOUT` for query embedding timeouts, and improved context assembly with detailed symbol information. The README and documentation have been updated to reflect these changes and provide clearer guidance on new commands and configurations.

Co-authored-by: Oğuz Öztürk <101019436+oztrkoguz@users.noreply.github.com>