MacOS shenenigans, add cross-compilation support for example

.gitignore

@@ -1 +1,3 @@
+.DS_Store
+
 /target

examples/docker-network/scripts/build.sh

@@ -1,5 +1,6 @@
 #!/bin/bash
 # Build the FIPS binary and copy it to the docker build context.
+# Supports cross-compilation from macOS to Linux using cargo-zigbuild.
 set -e
 
 SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
@@ -13,11 +14,42 @@ if [ ! -f "$PROJECT_ROOT/Cargo.toml" ]; then
     exit 1
 fi
 
-echo "Building FIPS (release)..."
-cargo build --release --manifest-path="$PROJECT_ROOT/Cargo.toml"
+# Detect host OS
+UNAME_S=$(uname -s)
+CARGO_TARGET="x86_64-unknown-linux-musl"
 
-echo "Copying binary to docker context..."
-cp "$PROJECT_ROOT/target/release/fips" "$DOCKER_DIR/fips"
+# Check for cross-compilation tooling on macOS
+if [ "$UNAME_S" = "Darwin" ]; then
+    echo "Detected macOS host - using cross-compilation for Linux..."
+    
+    # Check if cargo-zigbuild is installed
+    if ! command -v cargo-zigbuild &> /dev/null; then
+        echo "Error: cargo-zigbuild not found." >&2
+        echo "Please install it: cargo install cargo-zigbuild" >&2
+        echo "" >&2
+        echo "Or install zig directly: brew install zig" >&2
+        exit 1
+    fi
+    
+    # Check if target is installed
+    if ! rustup target list --installed | grep -q "$CARGO_TARGET"; then
+        echo "Installing Rust target $CARGO_TARGET..."
+        rustup target add "$CARGO_TARGET"
+    fi
+    
+    echo "Building FIPS for Linux (release) using cargo-zigbuild..."
+    cargo zigbuild --release --target "$CARGO_TARGET" --manifest-path="$PROJECT_ROOT/Cargo.toml"
+    
+    echo "Copying binary to docker context..."
+    cp "$PROJECT_ROOT/target/$CARGO_TARGET/release/fips" "$DOCKER_DIR/fips"
+else
+    # Native Linux build
+    echo "Building FIPS (release)..."
+    cargo build --release --manifest-path="$PROJECT_ROOT/Cargo.toml"
+    
+    echo "Copying binary to docker context..."
+    cp "$PROJECT_ROOT/target/release/fips" "$DOCKER_DIR/fips"
+fi
 
 echo "Done. Binary at $DOCKER_DIR/fips"
 echo ""