feat: add type stubs for cli, codegen, and security modules

openapi_first/cli.pyi

@@ -0,0 +1,7 @@
+from pathlib import Path
+
+DEFAULT_TEMPLATE: str
+
+def available_templates() -> list[str]: ...
+def copy_template(template: str, target_dir: Path) -> None: ...
+def main() -> None: ...