Release v0.4.0

Release version 0.4.0

Features:
- Add GUI file list with status tracking (not started, processing, processed)
- Add version and build time display in CLI and GUI
- Improve error handling with retry logic for Edge TTS API
- Fix macOS event loop issues
- Add rate limiting to avoid API limits
- Improve EPUB processor validation
- Fix path expansion for tilde (~) in file paths
- Add comprehensive EPUB tests
- Fix Windows build script