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

README.md

@@ -85,23 +85,23 @@ Three test files are included:
 - `Highlander-IMustFlipSmaller-OG.gif` - Animated GIF without transparency
 - `BTS-240-art.gif` - Animated GIF with transparency (1-bit alpha)
 
-## Cross-Compilation (Build for Linux/Windows from macOS)
+## Building Distributable Packages
 
-Build distributable packages for multiple platforms from a single machine.
+Build distributable packages for multiple platforms from a single macOS machine.
 
 ### Prerequisites
 
 ```bash
 # Install build tools
-cargo install cross cargo-deb cargo-generate-rpm
+cargo install cargo-bundle
 
-# Ensure Docker Desktop is installed and running
+# Ensure Docker Desktop is installed and running (for Linux/Windows builds)
 docker info
 ```
 
 ### Docker Configuration (Apple Silicon Mac)
 
-Before cross-compiling, configure Docker Desktop to share the Homebrew path:
+Before cross-compiling Linux/Windows targets, configure Docker Desktop to share the Homebrew path:
 
 1. Open Docker Desktop
 2. Go to **Settings** → **Resources** → **File Sharing**
@@ -111,10 +111,10 @@ Before cross-compiling, configure Docker Desktop to share the Homebrew path:
 ### Building
 
 ```bash
-# First-time setup: Build Docker images
+# First-time setup: Build Docker images (for Linux/Windows targets)
 ./scripts/build-all.sh --setup-docker
 
-# Build all targets
+# Build all targets (macOS, Linux, Windows)
 ./scripts/build-all.sh
 ```
 
@@ -124,9 +124,10 @@ After building, packages are in `dist/<version>/`:
 
 | Platform | Files | Notes |
 |----------|-------|-------|
-| Linux x86_64 | `.deb`, `.rpm`, `.tar.gz` | Cross-compiled |
-| Linux ARM64 | `.tar.gz` | Build natively on ARM64 Linux |
-| Windows x86_64 | `.zip` | Cross-compiled |
+| macOS | `.dmg`, `.app.zip` | Native build |
+| Linux x86_64 | `.deb`, `.rpm`, `.tar.gz` | Cross-compiled via Docker |
+| Linux ARM64 | — | Build natively on ARM64 Linux |
+| Windows x86_64 | `.zip` | Cross-compiled via Docker |
 
 **Note:** Linux ARM64 cross-compilation is disabled due to an upstream `zune-jpeg` NEON bug. Build ARM64 natively on a Linux ARM64 system.
 
@@ -150,6 +151,8 @@ avif-maker/
 │       ├── drop_zone.rs        # Drag-and-drop area
 │       ├── settings.rs         # Settings panel
 │       └── queue.rs            # Job queue display
+├── resources/
+│   └── AppIcon.icns            # macOS app icon
 ├── docker/                     # Cross-compilation Dockerfiles
 ├── scripts/
 │   └── build-all.sh            # Build script for all platforms