Update .gitignore and remove obsolete cleanup documentation - Added `.gradio` and `tests/data/cache` to `.gitignore` to prevent unnecessary file tracking. Deleted outdated cleanup documentation files (`AGENT_CLEANUP_COMPLETION.md` and `CLEANUP_PLAN.md`) to streamline the codebase and remove obsolete references. This cleanup supports ongoing refactoring efforts and enhances overall project maintainability.

Enhance PlannerAgent with entity recognition and coordination strategies - Implemented enhanced entity recognition and intent analysis in the PlannerAgent, allowing for improved query processing and coordination strategies. Updated the MusicRecommenderState model to include new fields for extracted entities, intent analysis, and conversation context. Enhanced logging and reasoning steps for better traceability during planning. Revised design documentation to reflect these changes and outline future enhancements.