Add window state persistence feature

## Summary Adds intelligent window state persistence to remember size, position, and maximized state between application sessions. ## Changes Made - Replaces always-maximized behavior with smart state restoration - Uses JSON file storage in app userData directory for cross-platform compatibility - Includes visual flash prevention during startup - Defaults to 1200x800 window size for first launch ## User Experience Improvement Previously, the app would always open maximized regardless of how the user sized the window. Now it: - Remembers exact window dimensions and position - Only opens maximized if it was closed maximized - Provides a better user experience by respecting user preferences ## Testing ✅ Window state persistence across app restarts ✅ Proper maximized state restoration ✅ Graceful fallback to defaults on first run ✅ No breaking changes to existing functionality See [CHANGES.md](https://github.com/gitobic/breadboard/blob/feature/documentation/CHANGES.md) for detailed technical implementation.