Add cross-compilation support for Linux and Windows

- Add Docker-based build system for cross-compiling on Apple Silicon
- Create Dockerfiles for Linux x86_64 and ARM64, Windows x86_64
- Add build-all.sh script for automated multi-platform builds
- Configure cargo-deb and cargo-generate-rpm for Linux packaging
- Update README with cross-compilation instructions

Supported outputs:
- Linux x86_64: .deb, .rpm, .tar.gz
- Windows x86_64: .zip

Note: Linux ARM64 disabled due to upstream zune-jpeg NEON bug

README.md

@@ -85,6 +85,51 @@ 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)
+
+Build distributable packages for multiple platforms from a single machine.
+
+### Prerequisites
+
+```bash
+# Install build tools
+cargo install cross cargo-deb cargo-generate-rpm
+
+# Ensure Docker Desktop is installed and running
+docker info
+```
+
+### Docker Configuration (Apple Silicon Mac)
+
+Before cross-compiling, configure Docker Desktop to share the Homebrew path:
+
+1. Open Docker Desktop
+2. Go to **Settings** → **Resources** → **File Sharing**
+3. Add `/opt/homebrew` to the shared paths
+4. Click **Apply & Restart**
+
+### Building
+
+```bash
+# First-time setup: Build Docker images
+./scripts/build-all.sh --setup-docker
+
+# Build all targets
+./scripts/build-all.sh
+```
+
+### Output
+
+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 |
+
+**Note:** Linux ARM64 cross-compilation is disabled due to an upstream `zune-jpeg` NEON bug. Build ARM64 natively on a Linux ARM64 system.
+
 ## Architecture
 
 ```
@@ -105,6 +150,9 @@ avif-maker/
 │       ├── drop_zone.rs        # Drag-and-drop area
 │       ├── settings.rs         # Settings panel
 │       └── queue.rs            # Job queue display
+├── docker/                     # Cross-compilation Dockerfiles
+├── scripts/
+│   └── build-all.sh            # Build script for all platforms
 └── Cargo.toml
 ```