Add GitHub Actions CI: auto-build for Windows + macOS

- Windows: VST3 + Standalone (x64, MSVC 2022)
- macOS: VST3 + AU + Standalone (Universal Binary: arm64 + x86_64)
- Auto-release: push a tag (e.g. v1.2) to create GitHub Release with all artifacts
- Added AU format to CMakeLists.txt (macOS Audio Unit)
- Builds on every push to main and on PRs

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.github/workflows/build.yml

@@ -0,0 +1,108 @@
+name: Build InstaDrums
+
+on:
+  push:
+    branches: [main]
+    tags: ['v*']
+  pull_request:
+    branches: [main]
+
+jobs:
+  build-windows:
+    runs-on: windows-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Clone JUCE
+        run: git clone --depth 1 https://github.com/juce-framework/JUCE.git ../JUCE
+
+      - name: Configure CMake
+        run: cmake -B build -G "Visual Studio 17 2022" -A x64
+
+      - name: Build Release
+        run: cmake --build build --config Release
+
+      - name: Package VST3
+        run: Compress-Archive -Path "build/InstaDrums_artefacts/Release/VST3/InstaDrums.vst3" -DestinationPath "InstaDrums-VST3-Win64.zip"
+
+      - name: Package Standalone
+        run: Compress-Archive -Path "build/InstaDrums_artefacts/Release/Standalone/InstaDrums.exe" -DestinationPath "InstaDrums-Standalone-Win64.zip"
+
+      - name: Upload VST3
+        uses: actions/upload-artifact@v4
+        with:
+          name: InstaDrums-VST3-Win64
+          path: InstaDrums-VST3-Win64.zip
+
+      - name: Upload Standalone
+        uses: actions/upload-artifact@v4
+        with:
+          name: InstaDrums-Standalone-Win64
+          path: InstaDrums-Standalone-Win64.zip
+
+  build-macos:
+    runs-on: macos-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Clone JUCE
+        run: git clone --depth 1 https://github.com/juce-framework/JUCE.git ../JUCE
+
+      - name: Configure CMake (Universal Binary)
+        run: cmake -B build -G Xcode -DCMAKE_OSX_ARCHITECTURES="arm64;x86_64" -DCMAKE_OSX_DEPLOYMENT_TARGET=11.0
+
+      - name: Build Release
+        run: cmake --build build --config Release
+
+      - name: Package VST3
+        working-directory: build/InstaDrums_artefacts/Release
+        run: zip -r $GITHUB_WORKSPACE/InstaDrums-VST3-macOS.zip VST3/InstaDrums.vst3
+
+      - name: Package AU
+        working-directory: build/InstaDrums_artefacts/Release
+        run: zip -r $GITHUB_WORKSPACE/InstaDrums-AU-macOS.zip AU/InstaDrums.component
+
+      - name: Package Standalone
+        working-directory: build/InstaDrums_artefacts/Release
+        run: zip -r $GITHUB_WORKSPACE/InstaDrums-Standalone-macOS.zip Standalone/InstaDrums.app
+
+      - name: Upload VST3
+        uses: actions/upload-artifact@v4
+        with:
+          name: InstaDrums-VST3-macOS
+          path: InstaDrums-VST3-macOS.zip
+
+      - name: Upload AU
+        uses: actions/upload-artifact@v4
+        with:
+          name: InstaDrums-AU-macOS
+          path: InstaDrums-AU-macOS.zip
+
+      - name: Upload Standalone
+        uses: actions/upload-artifact@v4
+        with:
+          name: InstaDrums-Standalone-macOS
+          path: InstaDrums-Standalone-macOS.zip
+
+  release:
+    if: startsWith(github.ref, 'refs/tags/v')
+    needs: [build-windows, build-macos]
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+    steps:
+      - name: Download all artifacts
+        uses: actions/download-artifact@v4
+        with:
+          path: artifacts
+
+      - name: Create Release
+        uses: softprops/action-gh-release@v2
+        with:
+          files: |
+            artifacts/InstaDrums-VST3-Win64/InstaDrums-VST3-Win64.zip
+            artifacts/InstaDrums-Standalone-Win64/InstaDrums-Standalone-Win64.zip
+            artifacts/InstaDrums-VST3-macOS/InstaDrums-VST3-macOS.zip
+            artifacts/InstaDrums-AU-macOS/InstaDrums-AU-macOS.zip
+            artifacts/InstaDrums-Standalone-macOS/InstaDrums-Standalone-macOS.zip
+          generate_release_notes: true

CMakeLists.txt

@@ -13,7 +13,7 @@ juce_add_plugin(InstaDrums
     NEEDS_MIDI_OUTPUT TRUE
     PLUGIN_MANUFACTURER_CODE Inst
     PLUGIN_CODE Idrm
-    FORMATS VST3 Standalone
+    FORMATS VST3 AU Standalone
     PRODUCT_NAME "InstaDrums"
     COPY_PLUGIN_AFTER_BUILD FALSE
 )