Add cross-platform GitHub Actions build workflow

[frogshead]

Summary

Add comprehensive CI/CD pipeline for building executables across all major platforms using GitHub Actions matrix builds.

Supported Platforms

• ✅ Linux x64 (x86_64-unknown-linux-gnu)
• ✅ Linux ARM64 (aarch64-unknown-linux-gnu)
• ✅ macOS x64 (x86_64-apple-darwin)
• ✅ macOS ARM64 (aarch64-apple-darwin)
• ✅ Windows x64 (x86_64-pc-windows-msvc)

Features

• Matrix builds: Parallel compilation across all platforms
• Cross-compilation: Proper toolchain setup for ARM64 Linux builds
• Caching: Cargo registry caching for faster subsequent builds
• Binary optimization: Automatic stripping of debug symbols
• Artifact management: 30-day retention of build artifacts
• Auto-releases: Automatic GitHub releases for git tags
• Manual dispatch: Ability to trigger builds manually

Workflow Triggers

• 🔄 Push to main branch
• 🔄 Pull requests to main
• 🏷️ Git tags starting with v* (creates releases)
• 🖱️ Manual workflow dispatch

Testing

• ✅ Tested ARM64 macOS cross-compilation locally
• ✅ Workflow validates YAML syntax
• ✅ Uses latest GitHub Actions best practices

Benefits

• User convenience: Pre-built binaries for all platforms
• Release automation: Tags automatically create releases with binaries
• CI validation: Ensures builds work across all targets
• Distribution ready: Optimized, stripped binaries ready for use

🤖 Generated with Claude Code