Add package to release workflow

.gitea/workflows/release.yml

@@ -40,6 +40,45 @@ jobs:
           VER="${GITHUB_REF_NAME#v}"
           dart tool/release_publish.dart "$GITHUB_REF_NAME" "dist/watch-together-$VER-linux-x64.tar.gz"
 
+  arch:
+    runs-on: ubuntu-latest
+    container: archlinux:latest
+    steps:
+      - name: Install Arch build deps
+        run: |
+          pacman -Syu --noconfirm --needed base-devel clang cmake flutter git \
+            gtk3 libepoxy mpv ninja pkgconf
+
+      - name: Checkout
+        run: |
+          git init -q .
+          git remote add origin "$GITHUB_SERVER_URL/$GITHUB_REPOSITORY.git"
+          git fetch -q --tags origin "$GITHUB_SHA"
+          git checkout -q --force FETCH_HEAD
+
+      - name: Build Arch package
+        run: |
+          useradd --create-home builder
+          chown -R builder .
+          runuser -u builder -- sh -c \
+            'cd deploy/arch && makepkg --cleanbuild --noconfirm --nodeps'
+
+      - name: Publish Arch package
+        if: startsWith(github.ref, 'refs/tags/v')
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          GITEA_TOKEN: ${{ secrets.GITEA_TOKEN }}
+          RELEASE_TOKEN: ${{ secrets.RELEASE_TOKEN }}
+        run: |
+          TOKEN="${RELEASE_TOKEN:-${GITHUB_TOKEN:-$GITEA_TOKEN}}"
+          test -n "$TOKEN"
+          set -- deploy/arch/*.pkg.tar.zst
+          test -f "$1"
+          curl --fail --show-error --request PUT \
+            --header "Authorization: token $TOKEN" \
+            --upload-file "$1" \
+            "$GITHUB_API_URL/packages/$GITHUB_REPOSITORY_OWNER/arch/core/x86_64"
+
   windows:
     # yuuka-windows: host-mode runner (no containers), runs as SYSTEM, has
     # git + VS 2022 Build Tools but no bash/python — PowerShell and Dart