Add macOS packaging with .dmg and .app bundle

- Add cargo-bundle configuration for macOS app bundle
- Create placeholder app icon (blue with "A" letter)
- Update build-all.sh to create .dmg and .app.zip
- Update README with new build output table

macOS packages:
- .dmg: Disk image for drag-to-Applications install
- .app.zip: Zipped app bundle alternative

scripts/build-all.sh

@@ -83,6 +83,31 @@ docker run --rm --platform linux/amd64 \
 zip -j "$DIST_DIR/avif-maker-$VERSION-windows-x86_64.zip" \
     target/x86_64-pc-windows-gnu/release/avif-maker.exe
 
+# macOS (native build)
+echo ""
+echo "Building macOS..."
+cargo build --release
+
+# Create .app bundle
+echo "Creating .app bundle..."
+cargo bundle --release
+
+# Find the .app bundle
+APP_PATH="target/release/bundle/osx/AVIF Maker.app"
+if [[ -d "$APP_PATH" ]]; then
+    # Create DMG
+    echo "Creating DMG..."
+    DMG_NAME="avif-maker-$VERSION-macos.dmg"
+    rm -f "$DIST_DIR/$DMG_NAME"
+    hdiutil create -volname "AVIF Maker" -srcfolder "$APP_PATH" -ov -format UDZO "$DIST_DIR/$DMG_NAME"
+    
+    # Also create a zip of the .app for those who prefer it
+    echo "Creating .app zip..."
+    (cd "target/release/bundle/osx" && zip -r "../../../../$DIST_DIR/avif-maker-$VERSION-macos.app.zip" "AVIF Maker.app")
+else
+    echo "Warning: .app bundle not found at expected path"
+fi
+
 echo ""
 echo "================================"
 echo "Build complete! Artifacts in $DIST_DIR/"