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.mod

@@ -10,7 +10,10 @@ require (
 
 require (
 	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/inconshreveable/mousetrap v1.1.0 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
+	github.com/spf13/cobra v1.10.2 // indirect
+	github.com/spf13/pflag v1.0.9 // indirect
 	github.com/tetratelabs/wazero v1.9.0 // indirect
 	golang.org/x/sys v0.37.0 // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect