feat: add Cobra CLI framework with root and version commands

[jakec-dev]

Summary

Integrates the Cobra CLI framework and establishes a production-ready command structure with proper error
handling, testing, and version management.

What's Changed

• Added Cobra v1.9.1 as the CLI framework dependency
• Implemented root command with help text and proper metadata
• Created version subcommand with build-time variable injection support
• Updated Makefile ldflags to inject version info into the correct package path
• Added comprehensive unit tests for CLI commands
• Updated README with basic usage examples

Implementation Details

Package Structure

internal/
cli/
root.go # Root command definition
root_test.go # Command tests
commands.go # Command registration
version.go # Version subcommand
version_test.go # Version command tests
version/
version.go # Version info with ldflags injection
cmd/
aws-local-sync/
main.go # Minimal entry point with error handling

Key Design Decisions

1. Manual Cobra implementation (no generator) for better control
2. Testable architecture with dependency injection (e.g., io.Writer for version command)
3. Clean error handling - commands return errors, main() handles output to stderr
4. Proper exit codes - 0 for success, 1 for errors
5. No global state except for ldflags version injection (standard Go pattern)

Testing

• All tests pass with go test ./...
• Version injection verified with make build && ./bin/aws-local-sync version
• Error handling tested for invalid commands
• Help text displays correctly when run without arguments

Checklist

• Cobra framework integrated as dependency
• Root command with appropriate metadata
• Version subcommand with build metadata support
• Proper exit code handling
• Error output to stderr
• Testable command structure
• Unit tests for all commands
• No runtime panics possible
• README updated with usage examples

[jakec-dev]

Closes #20