Feature: Add CI build

.github/workflows/arch-makepkg.yml

@@ -0,0 +1,50 @@
+name: Build Arch Linux Package
+
+on:
+  push:
+  pull_request:
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  makepkg:
+    name: Build with makepkg
+    runs-on: ubuntu-latest
+    container:
+      image: archlinux:base-devel
+    env:
+      PKGDEST: ${{ github.workspace }}/pkgdest
+      SRCDEST: ${{ github.workspace }}/srcdest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+      - name: Prepare pacman
+        run: |
+          pacman-key --init
+          pacman-key --populate archlinux
+          pacman -Syu --noconfirm --needed git base-devel sudo gnupg maven unzip
+      - name: Create build user
+        run: |
+          useradd -m builder
+          echo 'builder ALL=(ALL) NOPASSWD: ALL' >> /etc/sudoers.d/builder
+          chown -R builder:builder "$GITHUB_WORKSPACE"
+          install -d -m 0755 -o builder -g builder "$PKGDEST" "$SRCDEST"
+      - name: Import Cryptomator release signing key
+        run: |
+          sudo -u builder gpg --batch --keyserver hkps://keyserver.ubuntu.com --recv-keys 58117AFA1F85B3EEC154677D615D449FE6E6A235 || \
+            sudo -u builder gpg --batch --keyserver hkps://keys.openpgp.org --recv-keys 58117AFA1F85B3EEC154677D615D449FE6E6A235
+      - name: Build package with makepkg
+        run: |
+          sudo -u builder env \
+            PKGDEST="$PKGDEST" \
+            SRCDEST="$SRCDEST" \
+            makepkg --syncdeps --cleanbuild --noconfirm --log
+      - name: Upload package artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: arch-package-${{ github.run_number }}
+          if-no-files-found: error
+          path: |
+            ${{ env.PKGDEST }}/*.pkg.tar.zst