ci: add Arch Linux package build to desktop CI workflow

- Implement a new build step in `build-desktop-platforms.yml` to generate Arch Linux `.pkg.tar.zst` packages for the "modern" Linux target.
- Add logic to extract the project version from `gradle/libs.versions.toml` and locate the app binary directory.
- Create a standard Arch Linux package structure under `/opt/github-store` with a launcher symlink in `/usr/bin`.
- Include a `.desktop` entry, icon assets, and a generated `.PKGINFO` metadata file for `pacman` compatibility.
- Configure the workflow to upload the resulting `.pkg.tar.zst` file as a build artifact.

Author: rainxchzed

.github/workflows/build-desktop-platforms.yml

@@ -310,3 +310,104 @@ jobs:
           if-no-files-found: error
           retention-days: 30
           compression-level: 0
+
+      - name: Build Arch Linux package (.pkg.tar.zst)
+        if: matrix.label == 'modern'
+        run: |
+          set -euo pipefail
+
+          VERSION=$(grep 'projectVersionName' gradle/libs.versions.toml | head -1 | sed 's/.*= *"\(.*\)"/\1/')
+          PKG_NAME="github-store"
+          PKG_DIR="pkg-root"
+
+          # Find the app directory produced by packageAppImage
+          APP_ROOT=""
+          for candidate in \
+            composeApp/build/compose/binaries/main/app/GitHub-Store \
+            composeApp/build/compose/binaries/main/app-image/GitHub-Store; do
+            if [ -f "$candidate/bin/GitHub-Store" ]; then
+              APP_ROOT="$candidate"
+              break
+            fi
+          done
+
+          # Fall back to the AppDir we created earlier if still present
+          if [ -z "$APP_ROOT" ] && [ -f "GitHub-Store.AppDir/bin/GitHub-Store" ]; then
+            APP_ROOT="GitHub-Store.AppDir"
+          fi
+
+          if [ -z "$APP_ROOT" ]; then
+            echo "ERROR: Could not find app directory for Arch packaging"
+            exit 1
+          fi
+
+          # Build the package tree
+          mkdir -p "$PKG_DIR/opt/github-store"
+          cp -a "$APP_ROOT"/. "$PKG_DIR/opt/github-store/"
+
+          # Launcher symlink
+          mkdir -p "$PKG_DIR/usr/bin"
+          ln -s "/opt/github-store/bin/GitHub-Store" "$PKG_DIR/usr/bin/github-store"
+
+          # Desktop entry
+          mkdir -p "$PKG_DIR/usr/share/applications"
+          cat > "$PKG_DIR/usr/share/applications/github-store.desktop" << 'EOF'
+          [Desktop Entry]
+          Type=Application
+          Name=GitHub Store
+          Exec=/opt/github-store/bin/GitHub-Store
+          Icon=github-store
+          Categories=Development;
+          Comment=Cross-platform app store for GitHub releases
+          StartupWMClass=github-store
+          EOF
+          sed -i 's/^          //' "$PKG_DIR/usr/share/applications/github-store.desktop"
+
+          # Icon
+          if [ -f "$PKG_DIR/opt/github-store/lib/GitHub-Store.png" ]; then
+            mkdir -p "$PKG_DIR/usr/share/icons/hicolor/256x256/apps"
+            cp "$PKG_DIR/opt/github-store/lib/GitHub-Store.png" \
+               "$PKG_DIR/usr/share/icons/hicolor/256x256/apps/github-store.png"
+          fi
+
+          # .PKGINFO (pacman metadata — must be a flat file at archive root)
+          INSTALLED_SIZE=$(du -sb "$PKG_DIR" | cut -f1)
+          cat > "$PKG_DIR/.PKGINFO" << EOF
+          pkgname = ${PKG_NAME}
+          pkgver = ${VERSION}-1
+          pkgdesc = Cross-platform app store for GitHub releases
+          url = https://github.com/OpenHub-Store/GitHub-Store
+          builddate = $(date +%s)
+          packager = GitHub Actions
+          arch = x86_64
+          license = GPL-3.0
+          size = ${INSTALLED_SIZE}
+          depend = java-runtime>=21
+          depend = hicolor-icon-theme
+          EOF
+          sed -i 's/^          //' "$PKG_DIR/.PKGINFO"
+
+          # Create .pkg.tar.zst
+          sudo apt-get install -y zstd
+          OUTPUT_DIR="composeApp/build/compose/binaries/main/arch"
+          mkdir -p "$OUTPUT_DIR"
+          ARCHIVE="${PKG_NAME}-${VERSION}-1-x86_64.pkg.tar.zst"
+
+          cd "$PKG_DIR"
+          # .PKGINFO must come first in the archive
+          tar --zstd -cf "../${OUTPUT_DIR}/${ARCHIVE}" .PKGINFO opt usr
+          cd ..
+
+          echo "Created Arch package:"
+          ls -lh "${OUTPUT_DIR}/${ARCHIVE}"
+        shell: bash
+
+      - name: Upload Arch Linux package
+        if: matrix.label == 'modern'
+        uses: actions/upload-artifact@v4
+        with:
+          name: linux-arch
+          path: composeApp/build/compose/binaries/main/arch/*.pkg.tar.zst
+          if-no-files-found: error
+          retention-days: 30
+          compression-level: 0