Add CLI and config file support

cli/src/error-handler.ts

@@ -0,0 +1,20 @@
+function formatError(error: unknown): string {
+  let message: string;
+
+  if (error instanceof Error) {
+    message = error.message;
+  } else if (typeof error === "string") {
+    message = error;
+  } else {
+    message = "Unknown error";
+  }
+
+  return message;
+}
+
+export function handleError(error: unknown): never {
+  const errorMessage = formatError(error);
+  console.error(errorMessage);
+
+  process.exit(1);
+}