Scratchmark 1.8.0

New: Nix + AppImage Build Support

• Added Nix flake for reproducible builds
• Added GitHub Actions workflow for automatic AppImage generation
• AppImage now available for Linux distribution
• Users no longer need Nix to run Scratchmark

AppImage Download

Download the AppImage and run:
```bash
chmod +x Scratchmark-1.8.0-x86_64.AppImage
./Scratchmark-1.8.0-x86_64.AppImage
```

System Requirements:

• gtk4
• libadwaita-1
• gtksourceview-5

Ubuntu/Debian:
```bash
sudo apt install libgtk-4-1 libadwaita-1-0 libgtksourceview-5-0
```

Fedora:
```bash
sudo dnf install gtk4 libadwaita gtksourceview5
```

Arch Linux:
```bash
sudo pacman -S gtk4 libadwaita gtksourceview5
```