feat(docker): add Windows cross-compilation support via Docker

Add Dockerfile.windows and build-windows.sh for cross-compiling Windows executables
in a containerized environment. Includes documentation updates in README.md with
build instructions and troubleshooting tips for Windows builds.

docker-build/README.md

@@ -62,4 +62,67 @@ docker run --rm -it -v "$(pwd)/../build/linux-x86_64":/out palladium-builder:lin
 
 **Docker build issues:** Ensure Docker has sufficient resources and the daemon is running
 
-**Missing dependencies:** The Dockerfile installs all required build dependencies automatically
+**Missing dependencies:** The Dockerfile installs all required build dependencies automatically
+
+## Windows x86_64 Build
+
+### Overview
+
+This build creates Windows x86_64 executables using cross-compilation in a Docker container based on Ubuntu 20.04. The build process:
+
+1. **Builds a Docker image** (`palladium-builder:windows-ubuntu20.04`) containing MinGW-w64 cross-compilation toolchain
+2. **Copies the entire repository** into the container during image build
+3. **Cross-compiles for Windows** using the `depends` system with `x86_64-w64-mingw32` target
+4. **Outputs .exe files** to a mounted volume for host access
+
+### Quick Start
+
+```bash
+cd docker-build
+chmod +x build-windows.sh
+./build-windows.sh
+```
+
+Windows executables will be available in `../build/windows/` directory.
+
+### Prerequisites
+
+- Docker installed and running ([installation guide](https://docs.docker.com/get-docker/))
+- Sufficient disk space for the build process (at least 12 GB free)
+- Internet connection for downloading dependencies and MinGW-w64 toolchain
+
+### Produced Executables
+
+The following Windows executables are built and copied to the output directory:
+
+- `palladiumd.exe`: Main daemon
+- `palladium-cli.exe`: Command-line client
+- `palladium-tx.exe`: Transaction utility
+- `palladium-wallet.exe`: Wallet utility
+- `palladium-qt.exe`: GUI application (if Qt dependencies are available)
+
+### Output Directory
+
+Executables are placed in: `../build/windows/` (relative to the docker-build directory)
+
+### Cross-Compilation Details
+
+- **Target Triple**: `x86_64-w64-mingw32`
+- **Toolchain**: MinGW-w64 cross-compiler
+- **Dependencies**: Built using the `depends` system for Windows target
+- **Configuration**: Uses `CONFIG_SITE` for proper cross-compilation setup
+
+### Troubleshooting
+
+**Permission errors:** The build script automatically handles file permissions using host UID/GID
+
+**Build failed:** Run interactive container for debugging:
+```bash
+docker run --rm -it -v "$(pwd)/../build/windows":/out palladium-builder:windows-ubuntu20.04 bash
+```
+
+**Cross-compilation issues:** Ensure the MinGW-w64 toolchain is properly installed in the container
+
+**Missing .exe files:** Check that the configure script detected the Windows target correctly
+
+**Docker build issues:** Ensure Docker has sufficient resources and the daemon is running