Add macOS cross-compilation support for GuruRMM agent

Enables building macOS agents (Intel and Apple Silicon) on Linux server
without requiring Mac hardware. Successfully tested on M3 MacBook Air.

Changes:
- Configure rustls for macOS builds (easier cross-compilation)
- Keep native-tls for Windows/Linux (Windows 7 compatibility)
- Add osxcross linker configuration for both architectures
- Create build-macos.sh script for automated builds
- Document complete setup in MACOS_BUILD.md

Technical Details:
- Build server: 172.16.3.30 (Ubuntu 22.04)
- Toolchain: osxcross 1.5 with macOS SDK 14.5
- Targets: x86_64-apple-darwin, aarch64-apple-darwin
- Binary sizes: ~3.5M (Intel), ~3.1M (ARM64)
- Build time: ~90 seconds per target

Tested: Successfully connected to wss://rmm-api.azcomputerguru.com/ws
Agent ID: 6177bcac-e046-4166-ac76-a6db68a363ab

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

projects/msp-tools/guru-rmm/agent/build-macos.sh

@@ -0,0 +1,70 @@
+#!/bin/bash
+set -e
+
+# Build script for GuruRMM agent - macOS only
+# Supports: macOS (Intel & Apple Silicon)
+
+echo "=== GuruRMM Agent macOS Build ==="
+echo ""
+
+# Add osxcross to PATH
+export PATH="/opt/osxcross/target/bin:$PATH"
+
+# Source cargo environment
+source ~/.cargo/env
+
+# Set up cross-compilation environment variables for macOS
+export CC_x86_64_apple_darwin=x86_64-apple-darwin23.5-clang
+export AR_x86_64_apple_darwin=x86_64-apple-darwin23.5-ar
+export CC_aarch64_apple_darwin=aarch64-apple-darwin23.5-clang
+export AR_aarch64_apple_darwin=aarch64-apple-darwin23.5-ar
+
+# Output directory
+OUTPUT_DIR="$(dirname "$0")/dist"
+
+# Create output directory
+mkdir -p "$OUTPUT_DIR"
+
+# Get version from Cargo.toml
+VERSION=$(grep '^version' Cargo.toml | head -1 | cut -d'"' -f2)
+echo "Building GuruRMM Agent v$VERSION for macOS"
+echo ""
+
+# Function to build for a target
+build_target() {
+    local target=$1
+    local name=$2
+    local ext=$3
+    
+    echo "[INFO] Building for $name ($target)..."
+    cargo build --release --target $target
+    
+    local binary_name="gururmm-agent$ext"
+    local output_name="gururmm-agent-$name-v$VERSION$ext"
+    
+    cp "target/$target/release/$binary_name" "$OUTPUT_DIR/$output_name"
+    
+    # Create SHA256 checksum
+    cd "$OUTPUT_DIR"
+    sha256sum "$output_name" > "$output_name.sha256"
+    cd - > /dev/null
+    
+    # Get file size
+    local size=$(du -h "$OUTPUT_DIR/$output_name" | cut -f1)
+    echo "[SUCCESS] Built $output_name ($size)"
+    echo ""
+}
+
+# Build for macOS platforms
+echo "=== Building for macOS (Intel) ==="
+build_target "x86_64-apple-darwin" "macos-amd64" ""
+
+echo "=== Building for macOS (Apple Silicon) ==="
+build_target "aarch64-apple-darwin" "macos-arm64" ""
+
+echo ""
+echo "=== Build Complete ==="
+echo ""
+echo "Artifacts in: $OUTPUT_DIR"
+ls -lh "$OUTPUT_DIR"
+