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

docker/Dockerfile.linux-arm64

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+FROM --platform=linux/amd64 rust:1.85-bookworm
+
+# Install build dependencies and ARM64 cross-compiler
+RUN dpkg --add-architecture arm64 && apt-get update && apt-get install -y \
+    cmake \
+    nasm \
+    meson \
+    ninja-build \
+    gcc-aarch64-linux-gnu \
+    g++-aarch64-linux-gnu \
+    libc6-dev-arm64-cross \
+    && rm -rf /var/lib/apt/lists/*
+
+# Add the ARM64 target
+RUN rustup target add aarch64-unknown-linux-gnu
+
+# Configure cargo for cross-compilation
+ENV CARGO_TARGET_AARCH64_UNKNOWN_LINUX_GNU_LINKER=aarch64-linux-gnu-gcc
+ENV CC_aarch64_unknown_linux_gnu=aarch64-linux-gnu-gcc
+ENV CXX_aarch64_unknown_linux_gnu=aarch64-linux-gnu-g++
+
+WORKDIR /build

docker/Dockerfile.linux-x86_64

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+FROM --platform=linux/amd64 rust:1.85-bookworm
+
+# Install build dependencies for libavif, dav1d, and GUI
+RUN apt-get update && apt-get install -y \
+    cmake \
+    nasm \
+    meson \
+    ninja-build \
+    libx11-dev \
+    libxcursor-dev \
+    libxrandr-dev \
+    libxi-dev \
+    libgl1-mesa-dev \
+    libwayland-dev \
+    libxkbcommon-dev \
+    rpm \
+    && rm -rf /var/lib/apt/lists/*
+
+# Add the target
+RUN rustup target add x86_64-unknown-linux-gnu
+
+# Install packaging tools
+RUN cargo install cargo-deb cargo-generate-rpm
+
+WORKDIR /build

docker/Dockerfile.windows-x86_64

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+FROM --platform=linux/amd64 rust:1.85-bookworm
+
+# Install build dependencies and MinGW cross-compiler
+RUN apt-get update && apt-get install -y \
+    cmake \
+    nasm \
+    meson \
+    ninja-build \
+    mingw-w64 \
+    && rm -rf /var/lib/apt/lists/*
+
+# Add the Windows target
+RUN rustup target add x86_64-pc-windows-gnu
+
+# Configure cargo for cross-compilation
+ENV CARGO_TARGET_X86_64_PC_WINDOWS_GNU_LINKER=x86_64-w64-mingw32-gcc
+ENV CC_x86_64_pc_windows_gnu=x86_64-w64-mingw32-gcc
+ENV CXX_x86_64_pc_windows_gnu=x86_64-w64-mingw32-g++
+
+WORKDIR /build