Improves the application's icon handling by introducing multi-resolution
support, replacing a single PNG file with multiple resolution-specific icons.
- ✨ **Added** multiple resolution icons (16x16, 32x32, 48x48, 64x64, 256x256, 512x512).
- 🔄 **Updated** GUI setup to use multi-resolution icons for better scalability.
- 🗑️ **Removed** the old single-resolution `icon.png`.
This update ensures better compatibility and visual quality across
different platforms and screen resolutions.
Robert Honz