feat(publishing): add support for prebuilt AppImage package

This update enhances the publishing workflow by introducing a new
prebuilt AppImage package for Gitty, allowing users to install
the application without needing to compile from source. The
workflow now includes steps to generate and publish the binary
AUR package alongside the standard source package.

- Introduced PKGBUILD-bin for the prebuilt AppImage
- Updated workflow to handle both source and binary package publishing
- Enhanced README to guide users on installing the new package

PKGBUILD-bin

@@ -0,0 +1,45 @@
+# Maintainer: Christoph Brandau <c.brandau91@googlemail.com>
+
+pkgname=gitty-desktop-bin
+pkgver=2026.8.3
+pkgrel=1
+pkgdesc="A lightweight, modern Git client built with Tauri (prebuilt AppImage)"
+arch=('x86_64')
+url="https://git.cbsk-tech.de/Christoph/GitLite"
+license=('MIT')
+depends=('fuse2' 'git' 'webkit2gtk-4.1' 'gtk3' 'hicolor-icon-theme' 'libappindicator-gtk3' 'librsvg' 'xdotool')
+provides=('gitty-desktop')
+conflicts=('gitty-desktop')
+options=('!strip')
+
+_appimage="Gitty_${pkgver}_amd64.AppImage"
+_artifact_url="https://cdn.cbsk-tech.de/gitty/${pkgver}/${_appimage}"
+_tag=2026.8.3
+source=("${_appimage}::${_artifact_url}"
+        "gitty-desktop.png::${url}/raw/tag/${_tag}/src-tauri/icons/icon.png")
+sha256sums=('SKIP'
+            'SKIP')
+
+package() {
+  install -Dm755 "$srcdir/$_appimage" \
+    "$pkgdir/opt/$pkgname/gitty-desktop.AppImage"
+  install -d "$pkgdir/usr/bin"
+  ln -s "/opt/$pkgname/gitty-desktop.AppImage" \
+    "$pkgdir/usr/bin/gitty-desktop"
+
+  install -Dm644 "$srcdir/gitty-desktop.png" \
+    "$pkgdir/usr/share/icons/hicolor/512x512/apps/gitty-desktop.png"
+
+  install -d "$pkgdir/usr/share/applications"
+  cat > "$pkgdir/usr/share/applications/gitty-desktop.desktop" <<-EOF
+	[Desktop Entry]
+	Type=Application
+	Name=Gitty
+	Comment=$pkgdesc
+	Exec=gitty-desktop
+	Icon=gitty-desktop
+	Terminal=false
+	Categories=Development;RevisionControl;
+	StartupWMClass=gitty
+	EOF
+}