Fix thread safety for conversation history access

Add custom dictionary and improve conversation context strategy

Add conversation history context to LLM refinement

Fix clipboard restore logic and WaveformView timer leak

Add AI spinner animation and ephemeral URLSession with retry

Add LLM retry with exponential backoff and update README

Fix rapid Fn key press causing recording to hang

Add LLM request/response logging to project logs directory

Improve LLM prompt for better English term recognition in Chinese speech

Initial commit: macOS menu-bar voice input app