feat(cli): add cobra-based CLI with subcommands

Replace simple argument parsing with cobra to provide better CLI experience:

- Add 'execute' subcommand for running TypeScript files
- Add 'types' subcommand for printing TypeScript type declarations
- Add help text and error handling
- Update documentation with new usage examples

Add dependencies: github.com/spf13/cobra, github.com/spf13/pflag

go.sum

@@ -1,15 +1,24 @@
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