actions: Add workflow for building Windows/Linux packages

Add a GitHub Actions workflow that does MSVC builds for Windows packaged
into a zip and GCC builds for Linux packaged using Flatpak deployed as
artifacts. It also supports creating a release with the packages.

.github/workflows/build-release.yml

@@ -0,0 +1,173 @@
+name: Build and Release DeckTX
+
+on:
+  push:
+    branches: [ "main" ]
+  pull_request:
+    branches: [ "main" ]
+
+jobs:
+  build-windows:
+    runs-on: windows-latest
+
+    steps:
+    - uses: actions/checkout@v4
+      with:
+        submodules: true
+
+    - name: Set up CMake
+      uses: lukka/[email protected]
+
+    - name: Set environment variables
+      id: strings
+      run: |
+        echo "build-dir=${{ github.workspace }}/build" >> "$env:GITHUB_ENV"
+        echo "install-dir=${{ github.workspace }}/install" >> "$env:GITHUB_ENV"
+
+    - name: Configure CMake
+      run: cmake -B ${{ env.build-dir }} -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=${{ env.install-dir }} -S ${{ github.workspace }}
+
+    - name: Build
+      run: cmake --build ${{ env.build-dir }} --config Release --target install
+
+    - name: Package build artifacts
+      uses: actions/upload-artifact@v4
+      with:
+        name: DeckTX-Windows
+        path: ${{ env.install-dir }}
+
+  build-linux:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v4
+      with:
+        submodules: true
+
+    - name: Set up Flatpak
+      run: |
+        sudo apt update
+        sudo apt install -y flatpak flatpak-builder
+
+    - name: Add Flathub Remote
+      run: |
+        sudo flatpak remote-add --if-not-exists flathub https://flathub.org/repo/flathub.flatpakrepo
+
+    - name: Set environment variables
+      id: strings
+      run: |
+        echo "build-dir=${{ github.workspace }}/build" >> "$GITHUB_ENV"
+        echo "flatpak-json=${{ github.workspace }}/flatpak.json" >> "$GITHUB_ENV"
+        echo "flatpak-file=${{ github.workspace }}/decktx.flatpak" >> "$GITHUB_ENV"
+
+    - name: Allow file protocol in Git
+      run: git config --global protocol.file.allow always
+
+    - name: Generate Flatpak manifest
+      run: |
+        cat > ${{ env.flatpak-json }} <<EOL
+        {
+            "id": "com.pixelyion.DeckTX",
+            "runtime": "org.freedesktop.Platform",
+            "runtime-version": "23.08",
+            "sdk": "org.freedesktop.Sdk",
+            "command": "/app/DeckTX",
+            "modules": [
+                {
+                    "name": "DeckTX",
+                    "buildsystem": "cmake",
+                    "config-opts": [
+                        "-DCMAKE_BUILD_TYPE=Release"
+                    ],
+                    "build-options": {
+                      "build-args": [ "--share=network" ]
+                    },
+                    "sources": [
+                        {
+                            "type": "dir",
+                            "path": "."
+                        }
+                    ]
+                }
+            ],
+            "finish-args": [
+                "--share=network",
+                "--share=ipc",
+                "--device=dri",
+                "--socket=x11",
+                "--socket=wayland",
+                "--device=all"
+            ]
+        }
+        EOL
+
+    - name: Build Flatpak
+      run: |
+        mkdir -p ${{ env.build-dir }}/flatpak-decktx
+        sudo flatpak-builder --install-deps-from=flathub --force-clean --repo=repo ${{ env.build-dir }}/flatpak-decktx ${{ env.flatpak-json }}
+        flatpak build-bundle repo ${{ env.flatpak-file }} com.pixelyion.DeckTX
+
+    - name: Package build artifacts
+      uses: actions/upload-artifact@v4
+      with:
+        name: DeckTX-Linux
+        path: ${{ env.flatpak-file }}
+
+  release:
+    runs-on: ubuntu-latest
+    needs: [build-windows, build-linux]
+    if: github.event_name == 'push' && github.ref == 'refs/heads/main'
+    permissions:
+      contents: write
+    steps:
+    - uses: actions/checkout@v4
+
+    - name: Download Windows build artifacts
+      uses: actions/download-artifact@v4
+      with:
+        name: DeckTX-Windows
+        path: ${{ github.workspace }}/win
+
+    - name: Zip Windows build artifacts
+      run: |
+        cd ${{ github.workspace }}/win
+        zip -r ../decktx-windows.zip *
+
+    - name: Download Linux build artifacts
+      uses: actions/download-artifact@v4
+      with:
+        name: DeckTX-Linux
+        path: ${{ github.workspace }}
+
+    - name: Create Release
+      id: create_release
+      uses: comnoco/[email protected]
+      env:
+        GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+      with:
+        tag_name: ${{ github.ref }}
+        release_name: Release ${{ github.ref }}
+        body: |
+          Automatic release of DeckTX for tag ${{ github.ref }}.
+        draft: false
+        prerelease: false
+
+    - name: Upload Release Asset (Windows)
+      uses: actions/upload-release-asset@v1
+      env:
+        GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+      with:
+        upload_url: ${{ steps.create_release.outputs.upload_url }}
+        asset_path: ${{ github.workspace }}/decktx-windows.zip
+        asset_name: decktx-windows.zip
+        asset_content_type: application/zip
+
+    - name: Upload Release Asset (Linux)
+      uses: actions/upload-release-asset@latest
+      env:
+        GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+      with:
+        upload_url: ${{ steps.create_release.outputs.upload_url }}
+        asset_path: ${{ github.workspace }}/decktx.flatpak
+        asset_name: decktx-linux.flatpak
+        asset_content_type: application/vnd.flatpak